add /Account support

https://www.twilio.com/docs/api/rest/account
Merge pull request #29 from natebrennand/add_accounts

add /Account support
Merge pull request #31 from natebrennand/voice

prefix killing
fix calls post

closes #34
adding fixtures tests + updating examples
Merge branch 'master' of https://github.com/natebrennand/twilio-go into voice