Replace the C extension with a much better implementation

Special thanks to @nobu! I spent many hours on writing the extension and
ended up having +10000 lines of code, but he did it in 10mins with just
about 20 lines of code!
Update CHANGELOG [ci skip]
Version bump to 0.9.3
Fix JRuby build
Update CHANGELOG [ci skip]
Version bump to 0.9.4
Give a better name to the C extension
Update README [ci skip]