Searching is now optional and can be turned off.

By setting searchingEnabled to NO it does not add a search controller
to the tableview header.
Updated example view controller to show search controller
searchIsActive BOOL updated when the cancel button is pressed or when the search bar ends editing.
Potential fix for pull request #33
Added new init method in order not to break any older APIs
Put example class back to default init method.
Merge pull request #33 from steprescott/optional_search

Enable/disable search in FetchedResultsController