Mixpanel-py

* BACKWARD BREAKING CHANGE: Ignore source IP in events by default
* Allow users to provide "envelope" or "meta" tracking information

* New build
* Fix people analytics endpoint

* MANY BACKWARD COMPATIBILITY-BREAKING CHANGES.
* Name change- module is now named 'mixpanel'
* Introduction of pluggable Consumers
* Change to Mixpanel constructor- no longer takes a base url
* Addition of sample scripts in demo/ distribution directory
* rename of Mixpanel.track_charge to Mixpanel.people_track_charge
* New test suite

* Initial release