Fix #156: clear weak mods on every key press

- new macro_mods bit field for mods applied by macros
- weak_mods now only used for ACT_{L,R}MODS (i.e. LSFT, RSFT, LCTL etc.)
- clear the _weak_ mods on every key *pressed* such that LSFT etc.
  can no more interfere with the next key

tmk_core/common/action.c

@@ -70,6 +70,10 @@ void process_action(keyrecord_t *record)
 #endif
     dprintln();
 
+    if (event.pressed) {
+        // clear the potential weak mods left by previously pressed keys
+        clear_weak_mods();
+    }
     switch (action.kind.id) {
         /* Key and Mods */
         case ACT_LMODS:
@@ -500,6 +504,7 @@ void clear_keyboard(void)
 void clear_keyboard_but_mods(void)
 {
     clear_weak_mods();
+    clear_macro_mods();
     clear_keys();
     send_keyboard_report();
 #ifdef MOUSEKEY_ENABLE