pagerduty.coffee moved to it's own package

I've extracted this script to https://github.com/hubot-scripts/hubot-pager-me so it'd be a bit easier to manage adding people, releasing, refactoring, etc. I tried doing a filter-branch to extract and keep history, but had a tough time of it without having tons of empty merge commits :sweat: 

There's a few outstanding PRs that I'll see about porting over, with attribution cc https://github.com/github/hubot-scripts/pull/1458 https://github.com/github/hubot-scripts/pull/1280

cc previous contributors: @silas @gregone @ChrisLundquist @jacobbednarz  @streeter @jnewland @azizshamim