Add ability to specify the merge branch

For when you work off a branch other than master
Merge pull request #10 from mbarany/proon

Add ability to specify the merge branch
Add ipr: Issue Pull Request (in browser)
Merge pull request #11 from rhowardiv/ipr

Add ipr: Issue Pull Request (in browser)
Rebuild purq to not require API usage

Github pull requests are available under the target repo as
refs/pull/<PR#>/head. purq now takes advantage of this to work w/o
having to use the API (so no netrc or tokens required). Also much faster
this way.
Add todo for later
Merge pull request #12 from rhowardiv/purq-no-auth

Rebuild purq to not require API usage
Also stash untracked files before pr checks
Merge pull request #13 from rhowardiv/stashuntracked

Also stash untracked files before pr checks