Optimized OpenGL samplers binding
Optimized Renderer

Renderer was doing useless glActiveTexture calls
Updated CallOnExit

Made it non copyable
Made usage of std::function (thus allowing lambda to be used as
functions)
Improved sndfile Loader

When streaming and mixing to mono, the samples buffer is kept between
the calls
Made SoundBuffer loader exception-safe
Fixed sf_close not being called
Added File::Open(path, mode)
Improved sndfile loader implementation
Fixed LuaClass code
Made use of std::function
Fixed last commit
Removed Matrix4 "identity optimization"

Returned Matrix4 to a POD type
Made Shader::Send* ignore invalid location
Fixed instancing rendering

(Finally fixed that bug)
Lowered required instance count to ten
Updated comments
Optimized hardware buffers
Updated comments