Improved prePR

[zarthross]

I've found prePR to be a nice handy alias, but a little clumsy to extend. My team has been doing something similar for a while, but did a command alias in every project. I thought it would be nice if we had a handy easy way to extend the list of checks a developer should perform before submitting a pr so they have fewer painful moments realizing they forget a step and now their PR has failed.