Optional problem name (deducible from filename)

[ludopulles]

In cases where a filename like magicalmysteryknight.cpp obviously contains the problem name in it, one can simply type hattis magicalmysteryknight.cpp to submit this file for that problem. With --problemid a different name can still be supplied.

[EmilGedda]

Thank you for your PR!
Did not know anyone but me used hattis, so thats why the repo has been dormant for a while.
Sorry for not seeing this earlier, I will test it this later this weekend, I took a quick look and it looks solid, nice that you also remembered to update the Makefile generator.