Reduce key dictionary memory footprint

Instead of indexing `Key` objects that have multiple names by each
individual name, index by the set of names. This reduces the size of the
default key dictionary by a factor of between 2 and 3, and as result
also reduces reallocations/defragmentation.
Instead of instantiating all module/extension keys by default, append
them to the `maybe_key`-generator list.

kmk/modules/capsword.py

@@ -1,4 +1,5 @@
-from kmk.keys import FIRST_KMK_INTERNAL_KEY, KC, ModifierKey, make_key
+from kmk.handlers.stock import passthrough as handler_passthrough
+from kmk.keys import FIRST_KMK_INTERNAL_KEY, KC, ModifierKey, maybe_make_key
 from kmk.modules import Module
 
 
@@ -16,12 +17,16 @@ class CapsWord(Module):
         self._timeout_key = False
         self._cw_active = False
         self.timeout = timeout
-        make_key(
+        KC._generators.append(self.maybe_make_capsword_key())
+
+    def maybe_make_capsword_key(self):
+        return maybe_make_key(
             names=(
                 'CAPSWORD',
                 'CW',
             ),
             on_press=self.cw_pressed,
+            on_release=handler_passthrough,
         )
 
     def during_bootup(self, keyboard):