Ruby: generated foo.proto -> foo_pb.rb instead of foo.rb.

This brings us more into line with other langauges, and makes it more
obvious when we are requiring protobuf generated code.

Add a script to build protoc zip packages.

[ci skip]

Change-Id: Ia0e0bf3bb6bd24633dc8f294318bb20ac837f8b9

Ruby: translate package names from snake_case -> PascalCase.

Added unit test for PascalCasing package names in Ruby.

Added new file to ruby_EXTRA_DIST.