virtual npcs via showimg

[Aeva]

Some npcs can draw additional sprites, via 'showimg' and related commands. For example:

  showimg index, image.png, x, y;
  changeimgcolors index, red, green, blue, alpha;
  changeimgzoom index, scalefactor;

These are commonly used to add overhangs and lighting effects, so it would be good for the parser to be able to utilize these. The easiest way is to regex for the "showimg" command and for related commands that share the same index that have static arguments, and then to add a new source-less NPC that is pre-configured.