PR Automerging (#173)

Closes #109

* Add automerge definition

* Add mergeMethod

* add mergePr for GitHub

* update definitions

* autodetect merge type

* Check mergeable state

* Don’t split majors if automerging any

* Update mergePr api commands

* fix initRepo tests

* Add tests

* Fix mergePr call

* Fix description

* Revert branchWorker changes

* revert comment

* Add test

* Add major/minor separation tests

* Add status-success tests

* Add not-pending tests

* Add automerge tests

* Check branch status before merge