CHANGES(docs[deprecations]): Use Sphinx autodoc links for exceptions

why: Provide clickable documentation links for exception types.
what:
- Use {exc} role for DeprecatedError
- Use {class} role for DeprecationWarning

Author: tony

CHANGES

@@ -46,7 +46,7 @@ _Upcoming changes will be written here._
 
 #### APIs deprecated (#611)
 
-Legacy API methods now raise `libtmux.exc.DeprecatedError` (hard error) instead of emitting `DeprecationWarning`.
+Legacy API methods now raise {exc}`~libtmux.exc.DeprecatedError` (hard error) instead of emitting {class}`DeprecationWarning`.
 
 See {doc}`migration` for full context and examples.