Advanced time filtering

[benzkji]

Using git_time_extractor for estimating maintance work for a certain period would be quite usefull. So, some more switches:

--start-date=2015-06-01
--end-date=2015-06-30

what do you think?

[rietta]

I like the idea quite a lot.

[benzkji]

implementing it would mean shuffling some cmd line arguments, limit the commits needed for the calculations, then continue as usual? (you already have something similar with --year, right?)

[benzkji]

funny how I use time_extractor again and again, for various reasons...I'm more into python, but will try to mangle a PR anyway, sometime ;-)