Make OneShot.isStickable() overridable by user code

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

plugins/Kaleidoscope-OneShot/src/kaleidoscope/plugin/OneShot.cpp

@@ -118,7 +118,12 @@ bool OneShot::isSticky() {
 // could potentially use three different color values for the three
 // states (sticky | active && !sticky | pressed && !active).
 
+__attribute__((weak))
 bool OneShot::isStickable(Key key) {
+  return isStickableDefault(key);
+}
+
+bool OneShot::isStickableDefault(Key key) {
   int8_t n;
   if (key.isKeyboardModifier()) {
     n = key.getKeyCode() - Key_LeftControl.getKeyCode();

plugins/Kaleidoscope-OneShot/src/kaleidoscope/plugin/OneShot.h

@@ -153,7 +153,10 @@ class OneShot : public kaleidoscope::Plugin {
             key.getRaw() <= kaleidoscope::ranges::OS_LAST);
   }
 
-  static bool isStickable(Key key); // inline?
+  /// Determine if the given `key` is allowed to become sticky.
+  static bool isStickable(Key key);
+
+  static bool isStickableDefault(Key key);
 
   static bool isTemporary(KeyAddr key_addr); // inline?
   static bool isSticky(KeyAddr key_addr); // inline?