Add CellularAtomataMapGenerator

First pass at a cellular atomata map generator.

Add map.grid and a make_grid function to make it easier to make
numpy arrays for Map purposes.

Add ca.py to test the generator.

erynrl/map/grid.py

@@ -0,0 +1,10 @@
+# Eryn Wells <eryn@erynwells.me>
+
+import numpy as np
+
+from .tile import Empty
+from ..geometry import Size
+
+
+def make_grid(size: Size):
+    return np.full(size.numpy_shape, fill_value=Empty, order='F')