Add built in 'exit' command to git-repl

[wcmonty]

This just adds the ability to use exit to quit git-repl, in addition to the built-in quit.

[qw3rtman]

I'm good with this idea! For the actual code, instead of breaking exit and quit into two separate cases, you can combine them into one case like this:

quit|exit) break;;

Additionally, it would be nice to add this to the documentation here and update and regenerate the man page. 😄

[wcmonty]

@qw3rtman I updated the script to combine the cases in 554d779. The documentation has been updated in d6f505f.

[nicolaiskogheim]

The man page is not organised well now.

Git read-eval-print-loop belongs under Description, and the rest should go under Examples. The Options heading can be removed.

We should perhaps have a better description, but you don't need to do that now if you don't feel like it. The other changes is overdue so I would like that handled in this PR.

[nicolaiskogheim]

Too late, haha.

[qw3rtman]

@nicolaiskogheim Merged before I saw this. You can revert if you see fit.

[nicolaiskogheim]

Nah, I'll open a new one :) Should be quick to do.

[nicolaiskogheim]

Done #569