SetMesureText and SetQueryScrollOffset takes userData

[emoon]

Fixes #63

This is a breaking change due to new parameter. I set it to 0 in all cases except the SDL2 case where I used it as an example of passing the font data.

Another change now is because the userData is set inside the context object Clay_Initialize has to be called before calling this.

[nicbarker]

Thank you! I was literally implementing this last night 😁
I'll just implement passing the raylib fonts through in the same way as the SDL ones and we should be good to go.

Another change now is because the userData is set inside the context object Clay_Initialize has to be called before calling this.

Yeah, it's not super obvious the required order. Soon I think we'll change initialize to take a config struct that includes both the dimensions and the measure text function, which will get auto init to NULL if not provided 😁

[nicbarker]

Actually, I think it's fine to just merge this now and fix up the raylib example later - I'd like to switch the fontId to a uintptr_t anyway, as it's currently not very ergonomic to use.