Allow importing of homebrew material stored in a separate module.

examples/homebrew_campaign.py

@@ -0,0 +1,13 @@
+"""This file defines some homebrew mechanics that can be imported into
+character sheets using ``dungeonsheets.import_homebrew``. See
+``homebrew.py`` for an example of how these homebrew mechanics can be
+used.
+
+"""
+
+from dungeonsheets import mechanics
+
+
+class BrightSword(mechanics.Weapon):
+    """Give you enemies the old razzle-dazzle."""
+    name = "Brightsword"