[compiz] Fragment program API documentation

[Tomas Carnecky]

There is none!! And there are not even comments in the source code. Just
documenting the addXxxOpToFunctionData() would help immensely. I now
understand the API a bit thanks to the use of it in some plugins,  but
there are still open questions anyway.

What is addFetchOpToFunctionData() for? Does it fetch the color value
from the window texture?

tom