PHPactor works with file mapping

[EdwinHuijsing]

PHPactor did not work on remote machines like docker.

The PHPactor constructor needs the remote path, this is now handled.

Documentation updated.

[stale[bot]]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests. If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.