PLAutocompleteController now removes the autocomplete view when the cursor moves position.

The controller observes the NSTextViewDidChangeSelectionNotification and, if the selected range location moves backwards any distance or forward more than one character, the autocomplete view is hidden.
PLEditorViewController now uses the insertCompletion:forPartialWordRange:movement:isFinal method to insert a completion rather than insertText:.
PLTableView now posts a notification when its receives the mouseDown: message.
Fixed a minor inconsistency in the documentation for highlightSelectionInClipRect: method in PLTableView.
The text editor view now remains as first responder even when the table view is clicked.

The PLAutocompleteViewController registers for the PLTableViewDidReceiveMouseDown notification with the tableViewDidReceiveMouseDown: selector. In this method, it sets the textView as the first responder of the table view's window.