Add a civicrm_api3 wrapper

Per

http://forum.civicrm.org/index.php/topic,29219.0.html

the wrapper is something we agreed to make the api_v3 call signature more distinctive, remove the requirement for version and throw exceptions for errors.

The third of these we discussed a bit but I came around to it as a good pattern and decided if you don't want exceptions you should call the api using the traditional civicrm_api