Documentation drive

[xoft]

Well, almost. Mostly only the positive cases are explained, nothing is said about failures - what does GetWorld() return if the name is not found? Also, callbacks need their signatures explained - what should the callback function look like, what arguments it receives, what can it return?
I see I can improve my cWorld documentation by this, too. Shall we both improve ours?

Also, Lua doesn't distinguish between an int, a float or a double, it knows only a "number" type. (GetTotalChunkCount() etc.)