Add clear pair function

[nicocharlery]

Usage
Reset a user after having set a pair with git-pair.
There was a PR in the git-pair project that never got merged unfortunately

Run rcup to update configuration files once pulled locally.

Workflow

➜  platform git:(master) ✗ git config -l | grep user
user.name=Nicolas Charlery
user.email=nicolas@bokay.io

➜  platform git:(master) ✗ git pair TD
  Current author: Tetiana Dushenkivska
   Current email: nicolas.charlery+td@civilcode.io

➜  platform git:(master) ✗ git config -l | grep user
user.name=Nicolas Charlery
user.email=nicolas@bokay.io
user.name=Tetiana Dushenkivska
user.email=nicolas.charlery+td@civilcode.io

➜  platform git:(master) ✗ clear-pair
➜  platform git:(master) ✗ git config -l | grep user
user.name=Nicolas Charlery
user.email=nicolas@bokay.io

[nicholasjhenry]

@Bokay Now that we are using git authors we won't need this correct?

[nicocharlery]

@nicholasjhenry Correct!