Update exp.js

Add support for custom callback in recommendations

Add support for methods in loops

Merge pull request #73 from hackal/control-group-trigger

handle control_group tracking

Revert the formatter support in exp-bind

Add support for formatters in loops.

Fix exp-ref

Merge pull request #77 from hackal/onexit-trigger-fix

Onexit trigger fix

Merge pull request #77 from hackal/onexit-trigger-fix

Onexit trigger fix

Merge pull request #67 from hackal/bug-fix-arrow-function

Bug fix: Change exp-action event listener to arrow function