Ensure machine special method(s) include in generated docs

Without explicitly mentioning that it should have its docs
generated sphinx won't generate docs for it, so ensure that
we list __iter__ and __contains__ so that it does get
generated docs.

Also fixes 'default_start_state' docs which were not showing
up since they were on the setter method vs the getter method.

Change-Id: I83d02a3604678d16b16f6da5384ff10543af850f

automaton/machines.py

@@ -113,16 +113,16 @@ class FiniteMachine(object):
 
     @property
     def default_start_state(self):
-        return self._default_start_state
-
-    @default_start_state.setter
-    def default_start_state(self, state):
         """Sets the *default* start state that the machine should use.
 
         NOTE(harlowja): this will be used by ``initialize`` but only if that
         function is not given its own ``start_state`` that overrides this
         default.
         """
+        return self._default_start_state
+
+    @default_start_state.setter
+    def default_start_state(self, state):
         if self.frozen:
             raise excp.FrozenMachine()
         if state not in self._states:

doc/source/api.rst

@@ -11,6 +11,7 @@ Machines
 
 .. autoclass:: automaton.machines.FiniteMachine
     :members:
+    :special-members: __iter__, __contains__
 
 .. autoclass:: automaton.machines.HierarchicalFiniteMachine
     :members: