Check if pull request is targeted into correct branch.

This hook uses exclusively conventions from CKEditor 4 workflow:

• There are 2 main branches: master and major.
• All minor releases (x.y.z) are based on master branch.
• All major releases (x.y.0) are based on major branch.
• All PR-s are created from t/x branch, where x refers to the issue number.
• Every issue could have one of four allowed milestone values:
  • 4.x.y – next minor release; merged to master
  • 4.x.0 – next major release; merged to major
  • Backlog – done when it's done; merged to master
  • no milestone – done when it's done although it probably shouldn't be done; merged to master
• Based on the milestone of PR's parent issue, PR should be merged into appropriate branch (master or major).

Based on this conventions, it finds the PR's parent issue (via branch's name or PR's description) and determine appropriate branch using its milestone.

It needs 4 environment variables:

• GH_MSWH_SECRET – hook's secret
• GH_MSWH_TOKEN – personal token from repo's owner/administrator with at least repo:status scope
• GH_MSWH_OWNER – repo's owner
• GH_MSWH_REPO – repo's name

See LICENSE file for details.