[1.8.x] Documented Context.get() method.

Backport of 4d9414098b from master

docs/ref/templates/api.txt

@@ -415,6 +415,11 @@ dictionary syntax::
     >>> c['newvariable']
     'hello'
 
+.. method:: Context.get(key, otherwise=None)
+
+    Returns the value for ``key`` if ``key`` is in the context, else returns
+    ``otherwise``.
+
 .. method:: Context.pop()
 .. method:: Context.push()
 .. exception:: ContextPopException