[#1749] Merge PQM with squash.


Problem description
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With this new version PQM will merge branches with squash and will close the pull request.


Changes description
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when PQM commits the merge, it will also close the pull request with a small comment.

Added some brutal tests, but they require github authentication so I can not put the private credentials in the test.


How to try and test the changes
===============================

reviewers @alibotean 

Not sure how to test it... I think that we need to try to land this branch and see if it works :)