Merge pull request #39 from silverhammermba/fix_samples

Fix old method names, missing OGG file in samples
Updated README
Fixed copy paste error with outline color
Fixed intersection bug in rect
A lot of fixes for render target
Updated readme
Updated license
Updated SFML dependency
Weird fPIC flag had been included somehow, fixed now
Use latest build for samples, run without opengl

`require` latest build rather than latest installed version. This makes
it easier to test out samples for a new build without affecting the
currently installed rbSFML.

If opengl gem isn't installed, catch the LoadError and print an error,
so `rake samples` will still run.