Merge pull request #69 from nottombrown/master

Add track_charge and reset_charges to Mixpanel::Person
update Readme and Changelog
bump version
Add option to not render the mixpanel scripts.
Merge pull request #71 from mpereira/option-to-not-render-mixpanel-scripts

Add option to not render the mixpanel scripts.
Merge branch 'master' of github.com:zevarito/mixpanel
Add instructions for the insert_mixpanel_scripts option.
Merge pull request #72 from mpereira/add-instructions-for-insert-mixpanel-scripts-option

Add instructions for the insert_mixpanel_scripts option.
Merge branch 'master' of github.com:zevarito/mixpanel
update readme and changelog
bump version
Update to 2.2 snippet and API
Fix specs checking for Mixpanel script presence