Apply mutation in code changed in a diff

[brunoerg]

It would be very nice if we could have a flag for a diff file that universalmutator would use to create mutants only for the regions changed in the diff. It would be valuable to use this tool in CI/CD.

[agroce]

Again, sorry I didn't see this, very good idea. I hacked how to apply a patch to mutations in a way to avoid recomputing, but this just needs a little tool to pre-process to lines the way it does for TSTL coverage files. Good idea. I'm swamped the next week or two, but I'd like to get this done. Pretty small change, but very useful.