This eliminates a TODO(soon).

TODO:
- Rename Guarded to Bounded?
- Consider bounded array (where size and indexes are bounded quantities).
- Implement non-CAPNP_DEBUG_TYPES fallback.
  - Don't allow casting kj::maxValue to bounded type, this won't work right when not using debug types!
- Verify that this change doesn't hurt performance.

See: https://capnproto.org/news/2015-03-02-security-advisory-and-integer-overflow-protection.html

This commit as-is is the result of wading through two years of merge conflicts. It does not build as-is because new code added in that time hasn't been converted over.

Fixes #349.

You can now spawn a canonical message from:
* StructReader
* AnyStruct::Reader
* capnpc-c++ generated Foo::Reader

fixes #304

The user facing API is in MessageReader and MessageBuilder

{MessageBuilder,MessageReader}::isCanonical verifies the canonicity of a
message. This is both useful for debugging and for knowing if a received
message can be used for hashes, bytewise equality, etc.

MessageBuilder::canonicalRoot(Reader) can be used to write a canonical
message on a best effort basis, and checks itself using isCanonical.
It should succeed as long as the MessageBuilder in question:
* Has a first segment which is long enough to contain the message
* Has not been used before

Tests have been added in canonicalize-test.c++ which verify that for
crafted examples of canonicalization errors, isCanonical will reject,
and for a canonicalized version of the standard test message, it will
accept.

Also introduce a way to copy a struct or list which applies membranes to all embedded capabilities, since this seems like it will be needed in conjuction with the above.

**The problem**

The methods MessageReader::initCapTable() and MessageBuilder::getCapTable() always felt rather hacky. initCapTable() in particular feels like something that should be handled by the constructor. However, in practice, the cap table is often initialized based on a table encoded within the message itself. That is, an RPC message contains a "payload" which includes both the application-level message structure and a table of capabilities. The cap table has to be processed first, then initCapTable() is called on the overall message, before the application structure can safely be read.

The really weird part about this is that even though the cap table only applies to one branch of the message (the payload), it is set on the *whole* MessageReader. This implies, for example, that it would be impossible to have a message that contains multiple payloads. We haven't had any need for such a thing, but an implemnetation that has such artificial limitations feels very wrong.

MessageBuilder has similar issues going in the opposite direction.

All of this ugliness potentially gets worse when we introduce "membranes". We want a way to intercept capabilities as they are being read from or written to an RPC payload. Currently, the only plausible way to do that is, again, to apply a transformation to all capabilities in the message. In practice it seems like this would work out OK, but it again feels wrong -- we really want to take a single Reader or Builder and "wrap" it so that transformations are applied on capabilities read/written through it.

**The solution**

This change fixes the problem by adding a new pointer to each struct/list Reader/Builder that tracks the current cap table. So, now a Reader or Builder for a particular sub-object can be "imbued" with a cap table without affecting any other existing Readers/Builders pointing into the same message. The cap table is inherited by child Readers/Builders obtained through the original one.

This approach matches up nicely with membranes, which should make their implementation nice and clean.

This change unfortunately means that Readers and Builders are now bigger, possibly with some performance impact.

Fix bug where calling a list setter using a list obtained from a similarly-typed getter, but where the underlying pointer was null, would write an incorrectly-typed pointer in the destination (specifically, an empty List(Void)). Now it sets an empty list of the correct type.

AnyList::operator== is not inline but was declared as such. Also made formatting of operator declarations consistent.

Also fix AnyStruct::Reader/Builder as methods

The project file still only compiles a test binary, but it should be easy to separate out a library project from here.

Thanks again to Bryan Boreham <bjboreham@gmail.com> for much help getting this working.

This prevents the compiler from reporting warnings in these headers while compiling application code. Hopefully this will stem the never-ending stream of complaints from people who enable pedantic warnings.

To use, pass --disable-reflection to the configure script.

This produces a smaller runtime library. However, using it for this purpose is not recommended. The main purpose of lite mode is to define a subset of Cap'n Proto which might plausibly compile under MSVC. MSVC still lacks full support for constexpr and expression SFINAE; luckily, most of our use of these things relates to reflection, and not all users need reflection.

Cap'n Proto lite mode inherits its name from Protocol Buffers' lite mode. However, there are some key differences:

- Protobuf generated code included global constructors related to registering descriptors and extensions. For many people, this was the main reason to use lite mode: to get rid of these global constructors and achieve faster startup times. Cap'n Proto, on the other hand, never had global constructors in the first place.

- Schemas are actually still available in lite mode, though only in their raw (Cap'n Proto structure) form. Only the schema API (which wraps the raw schemas in a more convenient interface) and reflection API (which offers a convenient way to use the schemas) are unavailable.

- Lite mode is enabled in an application by defining CAPNP_LITE rather than by specifying an annotation in the schema file. This better-reflects real-world usage patterns, where you typically want to enable lite mode application-wide anyway.

- We do not build the lite mode library by default. You must request it by passing --disable-reflection to the configure script. Before you can do that, you must have a prebuilt Cap'n Proto compiler binary available, since the compiler can't be built without reflection.

- Relatedly, the lite mode library is built with the same name as the full library. This library is not intended to be installed. If anything it should be statically linked. But, mostly the option only exists on non-MSVC platform to give us a way to test that we haven't broken lite mode.

Note that embedded schema structures in generated code are still incorrect.

That is to say, whereas previously we would extend capnp::typeId<T>() to a new type by declaring a specialization of it for that type, now we instead have the type contain a nested class called _capnpPrivate which contains a `typeId` constant.

This is necessary because it is impossible to specialize a template for a type which is itself nested inside a template type. E.g. it's impossible to write a specialization `template <typename T> typeId<Foo<T>::Bar>()`; C++ simply doesn't support this. But with generics, Cap'n Proto will allow types to be nested inside templates, so we need this to work.

For portions currently copyright by Kenton (most of it), transfer copyright to Sandstorm Development Group, Inc. (Kenton's company).

The license change is practically meaningless, as MIT and BSD 2-clause are legally equivalent. However, the BSD 2-clause license is sometimes confused for its ugly siblings, BSD 3-clause and BSD 4-clause. The MIT license is more immediately recognizeable for what it is.

Rémy Blank and Jason Choy (the two non-trivial contributors) are on record as approving this change:

https://groups.google.com/d/msg/capnproto/xXDd2HUOCcc/gbe_COIuXKYJ

Extend totalSizeInWords() to also return a count of capabilities, which helps when a separate capability table needs to be allocated as well.  Use this in the RPC system.

Revamp concurrency model, part 1:  EventLoop no longer allows cross-thread event queuing, simplifying many things.  Capability clients are no longer thread-safe, so they don't have to be so const.  In the future, explicit ways to communicate between threads will be re-added, but threads will be treated more like separate vats that just happen to have a particularly fat pipe.  Upcoming:  Remove mutexes.