Add native jruby support to psych. Fixes #145

I'm able to run ```rake compile``` and ```rake test``` on jruby now and things mostly work. The only change I had to make was to ```PsychToRuby.java``` because https://github.com/tenderlove/psych/commit/2c644e184192975b261a81f486a04defa3172b3f moved the ```path2class``` method from ```Psych::Visitors``` to ```Psych::ClassLoader```. However, there are still 20 test failures. I'm guessing these are just because we haven't synced up the jruby extension with all of the recent development.