Initial attempt to merge internal_state with kmk_keyboard. Seems to work on Plank so far

kmk/extensions/__init__.py

@@ -0,0 +1,42 @@
+class InvalidExtensionEnvironment(Exception):
+    pass
+
+
+class Extension:
+    _enabled = True
+
+    def enable(self, keyboard):
+        self._enabled = True
+
+        self.on_runtime_enable(self, keyboard)
+
+    def disable(self, keyboard):
+        self._enabled = False
+
+        self.on_runtime_disable(self, keyboard)
+
+    # The below methods should be implemented by subclasses
+
+    def on_runtime_enable(self, keyboard):
+        pass
+
+    def on_runtime_disable(self, keyboard):
+        pass
+
+    def during_bootup(self, keyboard):
+        pass
+
+    def before_matrix_scan(self, keyboard):
+        '''
+        Return value will be injected as an extra matrix update
+        '''
+        pass
+
+    def after_matrix_scan(self, keyboard, matrix_update):
+        pass
+
+    def before_hid_send(self, keyboard):
+        pass
+
+    def after_hid_send(self, keyboard):
+        pass