Force direction:ltr for the Gallery widget. Fixes #34.
Enforce content-box box-sizing for the navigation and indicators.

This prevents unintended behavior if all elements are set to border-box
box-sizing by default, which is the case for Bootstrap 3.
Added documentation about event callbacks and instructions on how to add additional Gallery elements.
Fixed an error in the browser support function when the Gallery script is included in the document head.
Merge pull request #1 from blueimp/master

merge from upstream