ruby cleanups

- style updates based on feedback from @warmwaffles and @supernullset 
  - split classes into their own files
  - keep `murmur3` out of the `Kernel` namespace
  - `return` is for lame-os
  - utilize block form of `open`
  - use `attr_readers` rather than ivars where appropriate
- ruby fallback for when C extensions are useless (aka support jruby without java extension)