Add support for automerging without PR, Closes #177 

* update definitions and docs


* Add mergeBranch api

* support merge commit

* set automergeType

* Update API

* Refactor merge commit

* branch-push working

* Refactor branch

* Add back base tree

* Fix failing tests

* Update definitions and docs

* Fix automerge logic

* Test isBranchStale

* start mergeBranch test

* test mergeBranch branch-push throws

* more tests

* test unknown commit type

* pr tests

* Detect automerge in versions helper

* update tests for new automergeEnabled flag

* refactor pr logic

* complete pr worker tests

* branch automerge tests

* Update docs

* refactor branch automerge check