mail: clarify usage

i3pystatus/mail/__init__.py

@@ -22,7 +22,7 @@ class Mail(IntervalModule):
 !!i3pystatus.mail!!"""
 
     settings = (
-        ("backends", "List of backends (instances of i3pystatus.mail.xxx)"),
+        ("backends", "List of backends (instances of `i3pystatus.mail.xxx.Backend`)"),
         "color", "color_unread", "format", "format_plural",
         ("hide_if_null", "Don't output anything if there are no new mails"),
     )

i3pystatus/mail/imap.py

@@ -55,3 +55,5 @@ class IMAP(Backend):
             return len(conn.search(None,"UnSeen")[1][0].split())
         else:
             sys.stderr.write("no connection")
+
+Backend = IMAP

i3pystatus/mail/notmuchmail.py

@@ -23,3 +23,5 @@ class Notmuch(Backend):
     @property
     def unread(self):
         return notmuch.Query(self.db, "tag:unread and tag:inbox").count_messages()
+
+Backend = Notmuch

i3pystatus/mail/thunderbird.py

@@ -56,3 +56,5 @@ class Thunderbird(Backend):
     def unread(self):
         self.run()
         return len(self._unread)
+
+Backend = Thunderbird