override the existing one even for message types.

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

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

Reflect the change that protobuf should now only be supporting 2.6+ (I'd guess note python 3.x+ when its supported in implementation)

Refer to the Python Packaging User Guide for installing setuptools (and pip) instead of out of date telecommunity guide.

Including <sys/param.h> on Mac/iOS doesn't define __BYTE_ORDER so
PROTOBUF_LITTLE_ENDIAN was never being defined. This commit adds a check
for the __LITTLE_ENDIAN__ macro which is defined by clang and Apple gcc on
little endian architectures.

Support Ruby code generation only for proto3.

Update Ruby build setup to produce gems successfully. Include upb as a single .c / .h file.