Add missing LIBPROTOC_EXPORT to ruby generator

Updated to latest upb and added test for JSON map operation.

add #to_ary to RepeatedField

MSVC protoc compiler fix

Support oneofs in MRI Ruby C extension.

<stdint.h> is not part of the standard, so I've added a workaround.

https://github.com/google/protobuf/issues/87

Fix illegal C++ use of reinterpret_cast<> to cast between nullptr_t and a pointer

- A golden-file test that ensures protoc produces known-valid output.
- A Ruby test that loads that golden file and ensures it actually works
  with the extension.

This split strategy allows us to test end-to-end without needing to
integrate the Ruby gem build system and the protoc build system. This is
desirable because we do not want a gem build/install to depend on
building protoc, and we do not want building protoc to depend on
building and testing the gem.

Support for maps in the MRI C Ruby extension.

Include names.h as java_names.h in the opensource tree

This adds the Map container and support for parsing and serializing maps
in the protobuf wire format (as defined by the C++ implementation, with
MapEntry submessages in a repeated field). JSON map
serialization/parsing are not yet supported as these will require some
changes to upb as well.

Update python version / setuptools instructions

 Add __version__

Improved little endian byte order detection