Add missing protection methods

[bobeagan]

There are many methods missing from https://developer.github.com/v3/repos/branches/ that could be added. The hierarchy of these API routes could make the Api/Repository/Protection.php get a little messy so I'm open to suggestions on whether it makes sense to add everything there or to break it out somehow.

[bobeagan]

@Nyholm are you waiting on something specific before dropping the next release? Was hoping to make use of some of these without having to switch to using a branch in composer. Thanks!