docs: clean and update of the Source/ folder

[zarov]

Part of #968

I also deprecated heightMapWidth in profit of width which is the real name of the parameter in the creation of as WMS url. I don't know if I could also add the height property ? So we could have something like:

this.width = source.width || source.height || 256;
this.height = source.height || source.width || 256;

[gchoqueux]

thanks