Added MemoryManager::GetAllocationCount()
Added OpenGL::Delete[FrameBuffer|VertexArray]

Also renamed OpenGL::OnContextChange to OnContextChanged (since it
happens after the context change)
Also improved RenderTexture implementation
Improved OpenGL context implementation
Made Context::Create exception-safe
Improved comments
Made Renderer use OpenGL::DeleteVertexArray
Added OpenGL function loading

glVertexAttrib[I|L]Pointer
Also removed useless test (since unsigned can't be under zero..)
Fixed static_assert tests
Added support for double and integer attribute (VertexDeclaration)

Improved Renderer error handling
Improved RenderWindow context creation