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