Clipping size and position for PASTE, LOADIFF, SAVEIFF

[dansanderson]

Currently, PASTE will paste the entire clipboard region at an x,y coordinate. At some point, someone added "width" and "height" parameters to our documentation, but this is not implemented and does not seem to be derived from the C65 design documentation. It would be useful to implement a PASTE width and height that clips the graphic being pasted at the left or bottom edges, or pastes the full graphic if the width or height is larger than its size.

Currently, LOADIFF always loads an IFF to the top left corner of the screen, regardless of the size of the image being loaded. This could benefit from x, y, width, and height arguments that behave like PASTE, using the image data from disk.

SAVEIFF could be similarly enhanced with x, y, width, and height arguments to behave like GCOPY while saving to disk.

Alternatives considered
Some might desire width and height parameters to stretch the image, and not clip. Perhaps this could be another mode of these commands, selected with an argument. Clipping is proposed as the sole implementation or default.