Update usage.rst
Update usage.rst

* List all HTTP methods
* Update the error handling priority text
* Add link to error to exception cookbook entry
* Add link to the Twig provider documentation

RayRutjes/Silex,fhinkel/Silex,plotek/Silex,cgsmith/Silex,mTorres/Silex,RayRutjes/Silex,Xephi/Silex,fabpot/Silex,arduanov/Silex,gencer/Silex,mTorres/Silex,mathroc/Silex,plotek/Silex,cesarmarinhorj/Silex,beealone/Silex,fabpot/Silex,Xephi/Silex,romainneutron/Silex,romainneutron/Silex,SanderKnape/Silex,silexphp/Silex,cesarmarinhorj/Silex,lokhman/Silex,lokhman/Silex,mmauri04/Silex,beealone/Silex,jdreesen/Silex,fhinkel/Silex,mmauri04/Silex,jdreesen/Silex,romainneutron/Silex,arduanov/Silex,SanderKnape/Silex,cgsmith/Silex,mathroc/Silex