stash-pullrequest-builder-2.0

This version introduces some under the hood improvements and some changes to how job parameters are picked up from comments.

Summary of changes:

• Multiple jobs with different parameters can now be triggered in one go, instead of submitting one comment at a time and waiting for each to be picked up by the PR polling cycle before submitting the next.
• The parameters for each job are now picked up exclusively from the comment that triggered it. This contrasts with the previous behaviour, where all comments were considered and more recently specified parameters would override previous ones. This means that it won't be necessary to clear parameters explicitly in order to rerun a job without a parameter that was previously set.
• PR polling is now done by a pool of threads. The number of threads can be customized.
• The "Build Started" and "Build Finished" status messages are now posted as replies to the original comment that triggered the build. For jobs that are triggered without comments, the status messages are posted as new comments since there is no trigger comment to reply to.