Merge pull request #139 from Fox32/feature/set-vertex-buffer

Add a setVertexBuffer
Merge pull request #143 from Fox32/feature/debugdrawmanager-addquad

Add addQuad to debug draw manager
Merge pull request #145 from Fox32/feature/drawbuffers-performance

Improve drawbuffers performance
Merge pull request #146 from Fox32/feature/avoid-get-parameter

Avoid using getParameter in setConstant
Avoid more useProgram calls. If the program is already bound, do nothing.
Merge branch 'feature/avoid-use-program' into feature/combined