Scan for vcs repos and save, ignore feature, `add-from-fs`

[tony]

Allow scanning for repos with a find/ag.

$ vcspull scan [path]  # prompt to merge into config (creating backup first) or create new

Should allow ignore dirs/patterns. Be fast, leverage https://github.com/ggreer/the_silver_searcher if in PATH.

[pirhoo]

This would be awesome! In the meantime, I made this: https://gist.github.com/pirhoo/9f1f42ed73c929e1e19101356482daeb