Added utility function for sorting collections by descending values using _.sortBy with the values returned by the callback reversed. (only callback functions are currently supported, other callbacks can be supported as needed)
Simplified sortByDescending.
Renamed sortByDescending to imply that it is only for numeric sort values.
Added functionality for calling sortByDescendingNumeric with a property name instead of a callback. Added a test for this functionality.

Renamed utilities.js to utility.js
Added a test to verify the functionality for sorting by descending numbers using a callback instead of a property.
Merge pull request #16 from SamGraber/sort_by_descending

Sort by descending