Mention register_error_handler in errorhandler doc

The documentation for @errorhandler gives "app.error_handler_spec[None][404] = page_not_found" as an example for adding an error handler without the decorator.  However, register_error_handler appears to be the correct way to do this (added 0.7), and it eliminates the problems with modifying error_handler_spec directly.
Add Flask.config_class feature
api.rst: fix some spelling/typos
Merge pull request #799 from cvrebert/patch-1

api.rst: fix some spelling/typos
cleared up confusion for from_envvar
Fixed a documentation typo
Merge branch 'master' of github.com:mitsuhiko/flask
Update example for Apache FCGI config to use worker processes using FastCgiServer, along with some notes about FastCgiExternalServer
Fixed a typo
Merge pull request #800 from nZac/issue#783

cleared up confusion for from_envvar in docs
Fix #782 -- /tmp/ in tutorial
Merge pull request #808 from untitaker/issue782

Fix #782 -- /tmp/ in tutorial
Remove Werkzeug bug workaround from flask/app.py

According to the note in the comment, you had to check to make sure that the
defaults were not an empty dictionary because of a bug in Werkzeug pre-0.7.

Since Flask officially requires 0.7 or greater, we can remove this little
workaround.
Merge pull request #811 from rpicard/remove_options_workaround

Remove Werkzeug bug workaround from flask/app.py
Added line for 1.0
Added SESSION_REFRESH_EACH_REQUEST config option.

This also changes how sessions are being refreshed.  With the new
behavior set-cookie is only emitted if the session is modified or if the
session is permanent.  Permanent sessions can be set to not refresh
automatically through the SESSION_REFRESH_EACH_REQUEST config key.

This fixes #798.
Merge branch 'master' of github.com:mitsuhiko/flask
Fixed a test that broke on 3.x
Fix #815
Merge pull request #816 from untitaker/allowed_methods

Fix #815