Add information about where the warning ends

[fvictorio]

Right now processStr only indicates where the warning begins. This makes sense when reporting the errors in the console but for other things (e.g. highlighting) it's not enough information. We should also output the line and column where the warning ends. (And maybe also the length? This would be redundant if you have the line and columns for the beginning and the end and the source file, but it could be helpfull anyway.)