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.

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