By user request, added a --filter option to consider only branches matching the given regex.

This turns out to be how everybody uses the tool: to clean up after
their own branches.

Fixed the sort-by-commits option.
Switched back to async using forEachLimit() to improve speed.

Batch up branch processing to avoid opening too many files. There are
probably more opportunities for performance wins, but it runs well
enough for me now.
Prepping for release.
Some last cleanup of the older name.
Skip default branch pointers when considering branches.
BSD license.
That's the MIT license, you dork, and you wanted MIT anyway.