Various docstring fixes.

- Use r""" \* """
- transform plugins note to ..warning
- ' -> ` for cross-reference
- fix some "more than one target found for cross-reference" warnings

letsencrypt/interfaces.py

@@ -49,7 +49,7 @@ class IPluginFactory(zope.interface.Interface):
         """Inject argument parser options (flags).
 
         1. Be nice and prepend all options and destinations with
-        `~.option_namespace` and `~.dest_namespace`.
+        `~.common.option_namespace` and `~common.dest_namespace`.
 
         2. Inject options (flags) only. Positional arguments are not
         allowed, as this would break the CLI.