Smart Github Merge oleh Anojh G

This extension makes it so that for any PRs being merged into the main Heap repo's `master` branch, the button defaults to a regular merge. All other PRs being merged into a Heap branch (e.g. `develop`) will default to a "squash and merge".

Also, PR titles of squash-merges will always default to the PR title and include the PR number in them.