Add a dungeon level generator, which:
1. generates an infinite sequence of rectangular rooms within the
dimensions of the level
2. removes any duplicates from that sequence
3. Generates a graph from the delaunay triangulation of the centerpoints
of those rooms
4. Generates the minimum-spanning-tree of that delaunay triangulation,
with weights given by line length in points
5. Adds back a subset (default 10-15%) of edges from the delaunay
triangulation to the graph
6. Uses the resulting graph to draw corridors between the rooms, using a
random point on the near edge of each room to pick the points of the
corridors
Gormlaks now move 1/8th the speed of the character, which means we can
run away from them - yay!
Unfortunately this also introduces a bug where they'll eventually get
stuck and not do anything, so I'll be tackling that next.
Previously the isUnit function was falsely returning `True` for
positions that were one tile off in *either* direction from the
character, when it should've been *both*. Oops.
When gormlaks see the character, they step towards them and attack
dealing 1 damage when adjacent. Characters have hitpoints now, displayed
at the bottom of the game screen, and when the game is over they die.
