* Performance enhancements on JS side.  Some function looped over a larger set of elements then necessary.  
* New Feature: Added filter button.  Filter will only recognize assignments that are categorized.  You can add a category by editing an assignment already in the gradebook or when adding a new assignment.

git-svn-id: https://plugins.svn.wordpress.org/an-gradebook/trunk@1029735 b8457f37-d9ea-0310-8a92-e5e31aec5664