Convert featureType and elementType toLowerCase

Turns out elementType and featureType are case sensitive, where in the normal API this is not a problem.
delegates non custom events to google.map
Adds ability to listen for clicks on overlays

This PR adds the ability to pass a `click` option into the `drawOverlay`
method in order to perform some action when an overlay's DOM element is clicked.
An accompanying test has been added.

When adding complex markers to a map, ones that use custom HTML/CSS, for
instance, it is necessary to use overlays rather than markers. That being the
case, it is desirable that a developer be able to easily listen to click events
on those overlays the same as they would on a standard marker.
Merge pull request #311 from mikefowler/master

Adds ability to listen for clicks on overlays
Update version (0.4.12)
Add functionality to remove controls
Fix removal code
Add unit test for the internal state after removing controls
Allow unitSystem setting in travelRoute
Merge pull request #327 from amsross/master

Allow unitSystem setting in travelRoute
Update version
Merge branch 'master' of github.com:HPNeo/gmaps
Merge pull request #316 from stanhu/remove-controls

Add functionality to remove controls
Merge pull request #300 from tdantas/master

delegates non custom events to google.map
Update version
Merge branch 'master' of github.com:HPNeo/gmaps
Merge pull request #291 from koenpunt/patch-1

Convert featureType and elementType toLowerCase
Merge branch 'master' of github.com:HPNeo/gmaps
Update version (0.4.13)
Update .gitignore