Add "application" to glossary

Author: tilgovi

doc/glossary.rst

@@ -6,6 +6,15 @@ Glossary
 .. glossary::
    :sorted:
 
+   application
+      An application is an instance of :class:`annotator.App`. It is the primary
+      object that coordinates annotation activities. It can be extended by
+      passing a :term:`module` reference to its
+      :func:`~annotator.App.prototype.include` method. Typically, You will
+      create at least one application when using Annotator. See the API
+      documentation for :class:`annotator.App` for details on construction and
+      methods.
+
    hook
       A function that handles work delegated to a :term:`module` by the
       :term:`application`. A hook function can return a value or a