Extract XML documentation in a primitive but reasonably-effective way

Support enum forward decls in Objective C++

NS_ENUM changes defintion in Objective C++ based on the C++ spec being
compiled with, special case the one situation where it wouldn't support doing a
forward decl for the enum.

This could be tidied up significantly, and at some point we will want to parse the markdown and generate more appropriate XML - but this is definitely better than nothing.

Generated code changes coming in next commit.

Cleanups for newer Xcodes

Add (some) XML documentation to generated code

Fix Podspec version number

- Move up to 8.4 as the high simulator (assuming Xcode 6.4).
- Add cast to NSMutableDictionary so clang and resolve the selector.
- Add case for the newer static analyzer so it won't trigger a false warning.
- Update the "dictionary" interface to use "object" naming. Xcode 7+ has gotten
  more strict on the use of nonnull/nullable; combining that with the generic
  collection support; and the "dictionary" classes we created now collide with
  what the generic KeyValueCoding in the system headers triggering
  warnings/errors. Fix this and hopefully all future issue by renaming the
  methods to use "object" for the classes that have data types as objects
  instead of PODs. Taking this renaming hit now while ObjC is still in beta
  because it is a breaking change for any existing code.

A very small fix to silence some warnings.

This was released as `3.0.0-alpha-4.1`

(Generated code changes coming next...)

There are now summaries for:
- The Types nested class (which holds nested types)
- The file descriptor class for each proto
- The enum generated for each oneof

(Also fixed two typos.)

Generated code in next commit.

Also updated the Gemfile.lock since alpha-4 has been
pushed to RubyGems.

Change-Id: I8ddc5f125f28aa9a33c88dfe48251a75a877e1d3

Handled blocks being too small in arena.cc

Generate C# directory hierarchy with new option

Add GOOGLE_ATTRIBUTE_NOINLINE to GetArena() and GetMaybeArenaPointer(…

Add GOOGLE_ATTRIBUTE_NOINLINE to GetArena() and GetMaybeArenaPointer() methods. This is to avoid "unresolved link" errors in MSVC 2015 during Release build

Fix compile failures building protobuf DLLs on MSVC in Chromium's cod…

Refine check for unordered_{map|set} availability.

Small fixes

It isn't always, which causes problems when trying to put negative
values into the array with C++11.

Bazel expects all tests to do this.

Update objc script in generate_descriptor_proto.sh

Fix podspec by adding missing comma

Pack/Unpack implementation for Any.

We still need the JSON representation, which relies on something like a DescriptorPool to fetch message types from based on the type URL. That will come a bit later.
(The DescriptorPool comment in this commit is just a note which will prove useful if we use DescriptorPool itself.)

Fix Python 3.4 cpp implementation

Rename 'BYTE_SIZE' macro to 'GOOGLE_PROTOBUF_BYTE_SIZE'

Xcode raises warning that says "'BYTE_SIZE' macro redefined".
The original 'BYTE_SIZE' macro definition is here, for example:
'/Applications/Xcode/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/usr/include/mach/vm_param.h'