VAO is new object in modern GL API, which can split and manage vertex
buffer and attribute state. This is optional in GLES and is mandatory in
GL.
Also index buffer is faster then pass cpu data in GL draw call.
We prefer to build up a tiny compact engine at memory rather than compatibility,
this engine is not considerd for end-users but designed for middle-level framework
and some low-level users.
Thus, we won't consider 64bits data size,
use explicit 32 bits data until coming next upgrade...
Change-Id: I0704d5f1e0eb909cccc10922bc5972e115fbbcc0
