Linkify branch names in PRs about refined-github

[dylang]

I've fantasized about taking a two week vacation to fly to sf, get hired by Github, make this change, quit, fly home, and return to my job.

[lukehefson]

Wow. Feels pretty good to say that we've finally addressed #1: https://github.blog/changelog/2019-03-29-linking-branch-names-on-pull-request-headers/

Thanks as ever to this community. You are the BEST!

[helix84]

Thank you for this. I don't know you but I love you ❤️

I wrote about this issue to GitHub support 2.5 years ago.

[fregante]

That's great but... deleted branches aren't marked with strikethrough. e.g. #1799

busches:update-diff-settings is a link that leads to a 404 and this could be clearer.

RGH can still strike through this linke at the bottom of the page, for example:

[sindresorhus]

@helix84 😃I've asked GitHub for it previously too. So have many of my friends.

[paulmolluzzo]

@dylang get me one too while you're there. kthxbye