Merge pull request #96 from futurice/master

`feedback` option in configuration is now optional in favor of an event listener on `'feedback'` however I did not remove a check that a `feedback` function has been specified.
Warn about lack of `feedback` listener

If Feedback has been initialised but no listener has been added before nextTick then raise a debug warning as data may be lost.
Updated for v1.3.1
v1.3.1 Release