modholdandtap implementation

docs/modholdandtap.md

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+# ModHoldAndTap
+This module allows to immitate the behaviour of ATL+TAB or CMD+TAB, etc.  
+Basically, it will hold the mod and tap a key on a layer other than default layer. The mod will be released when any other key is pressed or the layer key is released.
+The key will do nothing when it is placed on the default layer
+
+
+## Enabling the module
+```python
+from kmk.module.modholdandtap import ModHoldAndTap
+modholdandtap = ModHoldAndTap()
+keyboard.modules.append(modholdandtap)
+keyboard.keymap = [
+    [
+        KC.MHAT(kc=KC.TAB, mod=KC.LALT),
+        KC.MHAT(KC.TAB, KC.LSFT(KC.LALT)),
+    ],
+]
+```
+
+## Keycodes
+
+|Key                      |Description                                    |
+|-------------------------|-----------------------------------------------|
+|`KC.MHAT(KC.key, KC.mod)`|holds the mod and taps the key                 |