Make EventManager portable

So far, we need to bypass application object for modules to emit
a event.  This make EventManager portable and easy to pass event
emitter.  This brings modules less coupled with application object.

doc/extdev/appapi.rst

@@ -147,7 +147,7 @@ Sphinx core events
 ------------------
 
 These events are known to the core.  The arguments shown are given to the
-registered event handlers.  Use :meth:`.connect` in an extension's ``setup``
+registered event handlers.  Use :meth:`.Sphinx.connect` in an extension's ``setup``
 function (note that ``conf.py`` can also have a ``setup`` function) to connect
 handlers to the events.  Example:
 

doc/extdev/builderapi.rst

@@ -38,3 +38,8 @@ Builder API
    .. automethod:: write_doc
    .. automethod:: finish
 
+   **Attributes**
+
+   .. attribute:: events
+
+      An :class:`.EventManager` object.

doc/extdev/envapi.rst

@@ -27,6 +27,10 @@ Build environment API
 
       Directory for storing pickled doctrees.
 
+   .. attribute:: events
+
+      An :class:`.EventManager` object.
+
    .. attribute:: found_docs
 
       A set of all existing docnames.

doc/extdev/utils.rst

@@ -29,3 +29,9 @@ components (e.g. :class:`.Config`, :class:`.BuildEnvironment` and so on) easily.
 
 .. autoclass:: sphinx.transforms.post_transforms.images.ImageConverter
    :members:
+
+Utility components
+------------------
+
+.. autoclass:: sphinx.events.EventManager
+   :members: