Respect VCS ignore files

[tavianator]

As suggested by @merwok: #8 (comment), we should implement a -vcsignore action. Related to #30 since conditionally respecting .gitignore would be very weird, it should be an on/off thing regardless of where it appears on the command line.

[dezza]

Subscribed! I like the way https://github.com/sharkdp/fd does it with a global $XDG_CONFIG_HOME/appname/ignore for stuff like /sys,/proc/,/dev/./run/,/mnt/ as well as btrfs /.snapshots and stuff