feat(grave-escape): implement grave-escape

closes #85

app/dts/behaviors.dtsi

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

app/dts/behaviors/gresc.dtsi

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <dt-bindings/zmk/keys.h>
+
+/ {
+	behaviors {
+		/omit-if-no-ref/ gresc: grave_escape {
+			compatible = "zmk,behavior-mod-morph";
+			label = "GRAVE_ESCAPE";
+			#binding-cells = <0>;
+			bindings = <&kp ESC>, <&kp GRAVE>;
+            mods = <(MOD_LGUI|MOD_LSFT|MOD_RGUI|MOD_RSFT)>;
+		};
+	};
+};

app/dts/bindings/behaviors/zmk,behavior-mod-morph.yaml

@@ -0,0 +1,16 @@
+# Copyright (c) 2020 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Keyboard Reset Behavior
+
+compatible: "zmk,behavior-mod-morph"
+
+include: zero_param.yaml
+
+properties:
+  bindings:
+    type: phandle-array
+    required: true
+  mods:
+    type: int
+    required: true