PLAutocompleteViewController now exposes a insertSelectedCompletion method rather than selectedCompletion.

This method inserts the remaining partial range of the selected completion into the text view. As helper methods to do this, the PLEditorViewController methods partialWordRange:atPosition: and previousWhitespacePosition:fromPosition: are moved into PLAutocompleteViewController. All of the logic for insertion that was in PLEditorViewController's textView:doCommandBySelector: method after receiving insertNewLine: has been moved into PLAutocompleteViewController.
The completionsInString:forPartialWordRange: in PLEditorViewController has been replaced with the delegate method textView:completions:forPartialWordRange:indexOfSelectedItem:.
PLAutocompleteViewController now calls the delegate method textView:completions:forPartialWordRange:indexOfSelectedItem: in order to retrieve and reload the autocomplete table.

The logic for this was in PLEditorViewController textStorageDidProcessEditing: and has been moved to the same method in PLAutocompleteViewController.
Refactored the PLAutocompleteViewController class methods partialWordRange:atPosition: and previousWhitespacePosition:fromPosition: as C functions.