Add Flask.config_class feature
Add ability to config from a JSON file
Update appfactories.rst, make extension related section clearer
Updated some typos

Fixed some incorrect variable references.
Makes the error names consistent
Don't refer to flaskext in docs
Merge pull request #886 from talam/patch-1

Updated some typos
Merge pull request #890 from seancron/documentation-fix

Documentation fix: Makes the error names consistent
Merge pull request #891 from ThiefMaster/docs-flaskext

Don't refer to flaskext in app.extensions docs
Clear exceptions when pushing a context

Fixes #882
Merge branch '0.10-maintenance'
Fix typo s/at at/at a/
Fix typo in docs for error_handler_spec
Merge pull request #895 from daybarr/patch-1

Fix typo in docs for error_handler_spec
URL Reversing in Quickstart #779

Updated quickstart to make clear that URL reversing refers to the use of
url_for() to build the URL. Issue #779
fix typo
Merge pull request #899 from pengfei-xue/master

fix typo(there-> their)
Changed the wording of some sentences there were difficult to understand.
Rewrapped lines
Update celery.rst

With the latest version of Celery (3.1.6), following this tutorial produces the following error when attempting to start the celery worker: 

    user_preload = tuple(self.app.user_options['preload'] or ())
AttributeError: 'Flask' object has no attribute 'user_options'

Using `app` as the variable name here confuses celery. Renaming `app` to `flask_app` in the tutorial solves the issue and allows the celery worker to start successfully.