Use glbinding instead of GLEW (closes #145)

[scheibel]

These commits remove GLEW as a dependency as well as OpenGL as compile time dependency.

Therefore, the following features were moved to glBinding:

• generated code for extension information
• before- and after-events for every OpenGL function

[scheibel]

Please test on Windows and OS X before merging this into master. Platform compatability should be provided through GLFW.