[Keyboard] Added A. Dux keyboard configurations (#14320)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Ryan <fauxpark@gmail.com>

keyboards/a_dux/keymaps/jcmkk3/oneshot.h

@@ -0,0 +1,46 @@
+/* Copyright 2021 @jcmkk3
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+#include QMK_KEYBOARD_H
+
+// Represents the four states a oneshot key can be in
+typedef enum {
+    os_up_unqueued,
+    os_up_queued,
+    os_down_unused,
+    os_down_used,
+} oneshot_state;
+
+// Custom oneshot mod implementation that doesn't rely on timers. If a mod is
+// used while it is held it will be unregistered on keyup as normal, otherwise
+// it will be queued and only released after the next non-mod keyup.
+void update_oneshot(
+    oneshot_state *state,
+    uint16_t mod,
+    uint16_t trigger,
+    uint16_t keycode,
+    keyrecord_t *record
+);
+
+// To be implemented by the consumer. Defines keys to cancel oneshot mods.
+bool is_oneshot_cancel_key(uint16_t keycode);
+
+// To be implemented by the consumer. Defines keys to ignore when determining
+// whether a oneshot mod has been used. Setting this to modifiers and layer
+// change keys allows stacking multiple oneshot modifiers, and carrying them
+// between layers.
+bool is_oneshot_ignored_key(uint16_t keycode);