MODDERS REJOICE! NEW GRAPHICS ARE EASY NOW!

appending extra images to the PCKs is cumbersome and difficult.
now, we can define extra graphics or replacements in the ruleset,
and the game will add them to the sprite sheets automagically.
Practical example of an "ExtraSprite"

an example of an ammendment to an existing file, and a commented example
of a user defined sprite sheet.

includes an alternative pathfinder sprite in case people don't like the orb.
use external sprites for pathfinder highlighting.

path is now shown for flying units.