WIP: Add initial restic support.

I've added a handler and example config file for restic. Since I'll be deploying this via Ansible, I'm not intending to write a helper, etc. But, I figured I'd share what basic progress I have made.

examples/example.restic

@@ -32,6 +32,9 @@ exclude =
 # This option may be specified multiple times.
 tag =
 
+# Only backup files from the file systems on which the initially specified files or directories reside.
+one_file_system = yes
+
 [retention]
 
 # Never delete the n last (most recent) snapshots