build: organize building system, support sphinx doc

Change-Id: I88ba0186a3defe1ffcbd55fb5f8ef81b5d2d3d81
docs: Add sphinx doc

Change-Id: Id709fdf3675a6057da75591e246112682a58d760
build: Do not warn about C99 extensions

Change-Id: I5729a29a0f415636fbe6aec0767a1d18618e7159