Add dragons, sans any interesting behaviour.
Fix spawn rates of fauna.

Increased for testing, forgot to put back.
Make dragons swarm the player, ridiculously.
Fix ghost dragon bits being left onscreen.
Hide from dragons in trees.
Make dragons use the right directional sprite.

Offset is still wrong for all angles not UPLEFT.
Fix dragon sprite offsets.
Give dragons a player-detection radius.
Make dragons behave less obsessively.
New file directions.py
Merge branch 'dragons'

Add dragons to the game.
Move diagonally over even solid terrain, and track the player similarly to bears.
Rename fire.{png,xcf} -> Fire to fit naming convention.
Split images.py - no file uses both HUD and tile images.