source branch regexp added

[micheelengronne]

Source branch regexp option added.

Answer #205

[aschmolck]

I would prefer for marge explicitly leaving a comment that it won't look at the MR when some MR gets assigned to it that is filtered out, because generally IMO this case reflects some error on part of the submitter or admin and the user may be confused why nothing is happening with their MR and suspect a problem with marge-bot.

Also, it would be nice to test the effect of the option, but given that the existing --branch-regexp doesn't do so either that's a bit of an ask (it also doesn't leave comments, but here the situation isn't symmetrical, since the main point of the branch filter is to speed things up by discarding irrelevant branches/repos straight away).

So I'm willing to merge this as is, if it's squashed and you have at least manually verified the behavior is what you expect.

[micheelengronne]

It was locally tested and it works.

[aschmolck]

Cool, merged -- thanks!