Add `rake test` task to run minitest specs
Add test coverage for the Color class

* Moved the extension to String outside of R2D namespace
Merge pull request #12 from JoelQ/first-test

Tests for `Color` class
Exception fixes
Added quadrilaterals
Added triangles
Add tests for the Image class
Merge pull request #13 from JoelQ/image-tests

Add tests for the Image class
Updates
Extracted from R2D module
Use `Image` instead of `R2D::Image`
Continued implementing Line
Add tests for the Line class
Merge pull request #14 from javichito/master

Add tests for the Line class
Implemented Image
Implemented Text
Continued implementing audio
Adapter and Window updates supporting Text, Image, and audio
Readme updates for newly implemented features
Removed old square tests