Updating from `v1` to `v2`

Breaking changes

v2 now expects repositories to be checked out with actions/checkout@v2

To use actions/checkout@v1 the following step to checkout the branch is necessary.
```
    - uses: actions/checkout@v1
    - name: Checkout branch
      run: git checkout "${GITHUB_REF:11}"
```
The two branch naming strategies have been swapped. Fixed branch naming strategy is now the default. i.e. branch-suffix: none is now the default and should be removed from configuration if set.
author-name, author-email, committer-name, committer-email have been removed in favour of author and committer. They can both be set in the format Display Name <email@address.com>

If neither author or committer are set the action will default to making commits as the GitHub Actions bot user.

Unpushed commits made during the workflow before the action runs will now be considered as changes to be raised in the pull request. See Controlling commits for details.
New commits made to the pull request base will now be taken into account when pull requests are updated.
If an updated pull request no longer differs from its base it will automatically be closed and the pull request branch deleted.