feature: scan changed files only

[mikeslattery]

ec -changed would be the same as:

ec $(git diff --name-only)

Also add as a configuration option, so it could be the default. I use ec for its speed and convenience, and this feature would further increase those.

It would also be nice if it used go-git so it didn't need to shell out.

[mstruebing]

That's a great suggestion!
Pull Requests are appreciated, I'm not sure when and if I find the time to implement this.

[sanmai-NL]

@mikeslattery I think such functionality is better separated into a dedicated tool, such as Lefthook.