Support exclude-regex

[mcico]

Hello,

I recently switched to use git-delete-merged-branches (from git-trim). I like the approach of git-dmb, in particular the safety net we get.

In #52 the support of --include-regex was added. I would appreciate the same feature, but for the exclusion.

In our company we work on many git repository (on many different projects), while we all follow a common branch naming pattern, where we for example use release/<version> as a pattern for branches we must keep for a longer time around.

Based on that I would like to add an --exclude-pattern which skips all branches of the given pattern, in my case release/.* from deletion. While I could add entries to the git config with a few bash commands, I would have to do that for each and every git repository and update it regularly, whereas with the pattern I could just add it to my global git config and be sure that such branches are not deleted by accident.

cheers & thanks, marco