Add dungeon level generation

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

build/hgeometry-fix-haddock.patch

@@ -0,0 +1,13 @@
+diff --git a/src/Data/Geometry/PlanarSubdivision/Merge.hs b/src/Data/Geometry/PlanarSubdivision/Merge.hs
+index 1136114..3f4e7bb 100644
+--- a/src/Data/Geometry/PlanarSubdivision/Merge.hs
++++ b/src/Data/Geometry/PlanarSubdivision/Merge.hs
+@@ -153,7 +153,7 @@ mergeWith' mergeFaces p1 p2 = PlanarSubdivision cs vd rd rf
+         -- we have to shift the number of the *Arcs*. Since every dart
+         -- consists of two arcs, we have to shift by numDarts / 2
+         -- Furthermore, we take numFaces - 1 since we want the first
+-        -- *internal* face of p2 (the one with FaceId 1) to correspond with the first free
++        -- /internal/ face of p2 (the one with FaceId 1) to correspond with the first free
+         -- position (at index numFaces)
+
+     cs = p1^.components <> p2'^.components