feat(sticky keys): initial implementation

app/dts/behaviors.dtsi

@@ -3,6 +3,7 @@
 #include <behaviors/none.dtsi>
 #include <behaviors/mod_tap.dtsi>
 #include <behaviors/layer_tap.dtsi>
+#include <behaviors/sticky_key.dtsi>
 #include <behaviors/momentary_layer.dtsi>
 #include <behaviors/toggle_layer.dtsi>
 #include <behaviors/reset.dtsi>

app/dts/behaviors/sticky_key.dtsi

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/ {
+	behaviors {
+		sk: behavior_sticky_key {
+			compatible = "zmk,behavior-sticky-key";
+			label = "STICKY_KEY";
+			#binding-cells = <1>;
+			release-after-ms = <1000>;
+			bindings = <&kp>;
+		};
+		sl: behavior_sticky_layer {
+			compatible = "zmk,behavior-sticky-key";
+			label = "STICKY_LAYER";
+			#binding-cells = <1>;
+			release-after-ms = <1000>;
+			bindings = <&mo>;
+		};
+	};
+
+};
+

app/dts/bindings/behaviors/zmk,behavior-sticky-key.yaml

@@ -0,0 +1,15 @@
+# Copyright (c) 2020 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Sticky key behavior
+
+compatible: "zmk,behavior-sticky-key"
+
+include: one_param.yaml
+
+properties:
+  bindings:
+    type: phandles
+    required: true
+  release-after-ms:
+    type: int