Add support for modules to exporting functions (@export decorator).

diff --git a/modules.py b/modules.py
index 5ea81cc..bd4eb17 100644
--- a/modules.py
+++ b/modules.py
@@ -15,9 +15,14 @@ from generate import *

 MODS_DIR = "modules"
 modules = {}
-exports = ['hook', 'intercept','themeable','theme',
+exports = ['export', 'hook', 'intercept','themeable','theme',
            'generates', 'generate', 'Generated']

+def export(func):
+  "Mark this function to export."
+  globals()[func.__name__] = func
+  return func
+
 @hook
 def module_load(name):
   global modules