Commands:

- transparent, no more args: interactive way for the user to specify the transparent color by a click
- transparent, idpath, #rrggbb: specify transparent color
- transparent, idpath, px, py: specify transparent color by pixel coordinates within the pixmap
- resize, no more args: interactive resizer where the user clicks on two points of the pixmap on screen and specifies the real disatnce between them and the code resizes the pixmap to match that
- resize, idpath, pdx, pdy, len: resize pixmap so that pixel distance pdx;pdy will match len coord units