Don't generate function implementation if already implemented

[lane-s]

In my opinion, the 'Generate Function Implementations' feature would be more useful if it skipped generating functions that are already implemented.

The workflow I'm imagining is this:
You write your header and generate initial implementations.
After doing some implementation, you realize you need a few more functions.
You go back to the header file and add the prototypes (I prefer doing it this way in order to add documentation by the prototypes before implementation).
You run the implementation generator again, but this time it only adds the new functions. It inserts them so that the order of functions in the cpp file and the header file are the same.

Does this sound feasible?