add protobuf support

[just-boris]

Protobuf is a binary format for data transfer.

This is an example how test file will look:

[zeitgeist87]

Thanks!

[zeitgeist87]

I renamed the language to protobuf. It would be nice if you could add an examples page examples/prism-protobuf.html and/or some test cases. We have a tutorial on how to create test cases: http://prismjs.com/test-suite.html