API docs for propka

- use autosummary (with custom module template)
- updated module docs for all modules so that they are included
  with sphinx autodocs

propka/coupled_groups.py

@@ -1,4 +1,10 @@
-"""Describe coupling between groups."""
+"""
+Coupling between groups
+=======================
+
+Describe and analyze energetic coupling between groups.
+"""
+
 import itertools
 import propka.lib
 from propka.group import Group