docs: Disambiguate references to Context

This addresses an error found while running tox -edocs

Warning, treated as error:
mitogen/docs/api.rst:469:more than one target found for cross-reference
u'Context': mitogen.core.Context, mitogen.parent.Context

docs/api.rst

@@ -458,7 +458,7 @@ Router Class
             rich data structures that cannot normally be passed via a
             serialization.
 
-        :param Context via:
+        :param mitogen.core.Context via:
             Same as the `via` parameter for :meth:`local`.
 
         :param bool debug:
@@ -1078,7 +1078,8 @@ Select Class
         each, returning the result of calling `msg.unpickle()` on each in turn.
         Results are returned in the order they arrived.
 
-        This is sugar for handling batch :class:`Context.call_async`
+        This is sugar for handling batch
+        :meth:`Context.call_async <mitogen.parent.Context.call_async>`
         invocations:
 
         .. code-block:: python
@@ -1245,7 +1246,8 @@ Broker Class
     .. method:: keep_alive
 
         Return :data:`True` if any reader's :attr:`Side.keep_alive`
-        attribute is :data:`True`, or any :class:`Context` is still
+        attribute is :data:`True`, or any
+        :class:`Context <mitogen.core.Context>` is still
         registered that is not the master. Used to delay shutdown while some
         important work is in progress (e.g. log draining).
 

docs/getting_started.rst

@@ -208,7 +208,7 @@ started the context, however as shown, this can be overridden.
 Calling A Function
 ------------------
 
-.. currentmodule:: mitogen.master
+.. currentmodule:: mitogen.parent
 
 Now that some contexts exist, it is time to execute code in them. Any regular
 function, static method, or class method reachable directly from module scope