remove exact statuscode checks

closes #35
fix comment
Merge pull request #39 from natebrennand/fixes

remove exact statuscode checks
add notifcation resource

https://www.twilio.com/docs/api/rest/notification
add example and make fixes
add another notification example
Merge pull request #41 from natebrennand/notification

add notification resource
Making twiml.Response implement http.Handler
Adding xml caching to twiml.Response