Added 2.3 upgrade notes containing app_dev.php changes regarding debug component.
merged branch pinkeen/master (PR #561)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #561).

Discussion
----------

Added 2.3 upgrade notes

After upgrading to symfony-2.3 I noticed that the debugging was crippled. I could not find anything in the upgrade notes, so here it is. I am not sure if I phrased it correctly.

PS Yes, I know, I should've subscribed symfony blog ages ago. I did so now.

Commits
-------

bdad65c Added 2.3 upgrade notes containing app_dev.php changes regarding debug component.
udpated the CHANGELOG for 2.3
Use kernel.http_method_override parameter
merged branch jeromemacias/use_http_method_override_parameter (PR #562)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #562).

Discussion
----------

Use kernel.http_method_override parameter

Commits
-------

fa99d80 Use kernel.http_method_override parameter
Merge branch 'old-2.3' into 2.3
Removed twig from dependencies as it is already included with symfony