Ruby 2.0.0

# New Features
* Language core features
- Keyword arguments, which give flexibility to API design
- Module#prepend, which is a new way to extend a class
- A literal %i, which creates an array of symbols easily
- __dir__, which returns the dirname of the file currently being executed
- The UTF-8 default encoding, which make many magic comments omissible
* Built-in libraries
- Enumerable#lazy and Enumerator::Lazy, for (possibly infinite) lazy stream
- Enumerator#size and Range#size, for lazy size evaluation
- #to_h, which is a new convention for conversion to Hash
- Onigmo, which is a new regexp engine (a fork of Oniguruma)
- Asynchronous exception handling API
* Debug support
- DTrace support, which enables run-time diagnosis in production
- TracePoint, which is an improved tracing API
* Performance improvements
- GC optimization by bitmap marking
- Kernel#require optimization which makes Rails startup very fast
- VM optimization such as method dispatch
- Float operation optimization