Fix warnings and code styling in the doc

There was a blank line missing that was generating a warning when
building the doc. Also, a removed function from cli.py was left in api.rst
(without_appcontext specifically) so this was also generating warnings.

Also corrects the format for a code block and adds a link to Werkzeug's Headers
class.

docs/api.rst

@@ -142,7 +142,7 @@ Response Objects
 
    .. attribute:: headers
 
-      A :class:`Headers` object representing the response headers.
+      A :class:`~werkzeug.datastructures.Headers` object representing the response headers.
 
    .. attribute:: status
 
@@ -771,11 +771,10 @@ Command Line Interface
 .. autofunction:: with_appcontext
 
 .. autofunction:: pass_script_info
+
    Marks a function so that an instance of :class:`ScriptInfo` is passed
    as first argument to the click callback.
 
-.. autofunction:: without_appcontext
-
 .. autofunction:: script_info_option
 
    A special decorator that informs a click callback to be passed the

flask/testing.py

@@ -54,6 +54,8 @@ class FlaskClient(Client):
         the test client uses.  Once the with block is left the session is
         stored back.
 
+        ::
+
             with client.session_transaction() as session:
                 session['value'] = 42