CRuby extensions post 0.6.0 release.

## NOT READY TO MERGE

Implemented the experimental CRuby branches into master after the 0.6.0
release. The experimental CRuby features were built over many, many commits
across several branches. Rather than interleave the commit history I
decided to start clean. A new branch was created and all new files were
copied in. All changed files were merged one by one. This single commit
now includes the following features:

* Gemspec configured for C-native extensions
* Rake tasks for building native extensions
* Script for building the extension that excludes non-supported Rubies
* CAtomicBoolean
* CAtomicMutex
* CEvent