Upgrade Ohcount to support ruby 1.9.x

* Includes Robin's work on updating SWIG bindings and patching ruby string encoding
* Build script is updated to automatically find the appropriate path for `ruby.h` file
* SourceFileTest already has the tests to assert valid encoding
* Verified on CentOS 5 and Ubuntu 12.04
* Fixed deprecation warnings and errors for SWIG 2.0.11
* <b>NOTE:</b> Supporting SWIG (2.0.11) will break Ohcount's backward compatibility with ruby 1.8.7. Or we can stick to SWIG (2.0.4) which will leave Ohcount still compatible with ruby 1.8.7. So its upto us to decide on which way we want it to be. Considering that ruby 1.8.7 has been retired, I would like to go with the hard upgrade option.
* Updated README