Total library rewrite

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Total library rewrite.
Main goals are compatibility with latest Ruby (2.1.2), total architecture remake and old API compatibility.

1. Extracted and refactored each ruby integration method to separate class.
2. Rewritten GSL and Ruby wrappers for integrate method.
3. Rewritten specs to support new syntax. Cleared specs.
4. Updated Readme to markdown, added instruction for GSL usage (rb-gsl is now runtime dependency)
5. Added bundler support (Added Gemfile)
6. Made gem with bundle gem command (for simple rake release)
7. Added travis-ci