Implement the afterSelect callback.

The new afterSelect callback on elemicaSuggest is invoked after the user
makes a selection from the suggestion box. It will pass in the entire
suggestion object representing the choice made by the user.
Invoke afterSelect callback with null after a selection is cleared.
Add a blurb to README about afterSelect.
Add a header comment for telling differences between versions.
Define a noop function.
Spec for afterSelect on identical selection.
Call out behavior of identical selections in README.
Merge pull request #10 from elemica/selection-made

Selection made: Add an afterSelect callback.

This is a bit of yak-shaving related to some parallel work going on in-house. This PR adds
an afterSelect parameter to the elemicaSuggest method. This parameter is defined as a
function that is used as follows:
 - When the user selects a suggestion, the afterSelect is invoked with the selected
   suggestion's JSON object.
 - When the user clears a selection, afterSelect is invoked with null passed in place of a
   suggestion object