Merge pull request #7 from bernstein/master

Remove <CL/cl_fwd.hpp> include.
Add occlusion query to query objects. Adjust render_device.h & .cpp, constants & forward headers accordingly.
add prefix 'OQMODE_' to occlusion query enums
Merge pull request #9 from Nyran/master

Add prefix 'OQMODE_' to occlusion query enums