Add PullRequestInfo with extra details

Pass more details about the pull request through to jenkins. Refactor with
new PullRequestInfo type constructed from the json api response to simplify
the passing around of details about pull requests.
Merge pull request #15 from bz2/kick_merge_extra_args

Add PullRequestInfo with extra details

Pass more details about the pull request through to jenkins. Refactor with
new PullRequestInfo type constructed from the json api response to simplify
the passing around of details about pull requests.