Adding ComboLayers to Layers Module (See #658) (#666)

---------

Co-authored-by: xs5871 <60395129+xs5871@users.noreply.github.com>

docs/en/combo_layers.md

@@ -0,0 +1,98 @@
+## Combo Layers
+
+Combo Layers is when you hold down 2 or more KC.MO() or KC.LM() keys at a time, and it goes to a defined layer.
+
+By default combo layers is not activated. You can activate combo layers by adding this to your `main.py` file.
+The combolayers NEEDS to be above the `keyboard.modules.append(Layers(combolayers))`
+
+```python
+combo_layers = {
+  (1, 2): 3,
+   }
+keyboard.modules.append(Layers(combo_layers))
+```
+
+In the above code, when layer 1 and 2 are held, layer 3 will activate. If you release 1 or 2 it will go to whatever key is still being held, if both are released it goes to the default (0) layer.  
+You should also notice that if you already have the layers Module activated, you can just add combolayers into `(Layers())`
+
+You can add more, and even add more than 2 layers at a time.
+
+```python
+combo_layers = {
+  (1, 2): 3,
+  (1, 2, 3): 4,
+  }
+```
+
+## Limitations
+
+There can only be one combo layer active at a time and for overlapping matches
+the first matching combo in `combo_layers` takes precedence.
+Example:
+```python
+layers = Layers()
+layers.combo_layers = {
+  (1, 2, 3): 8,
+  (1, 2): 9,
+  }
+keyboard.modules.append(Layers(combo_layers))
+```
+* If you activate layers 1 then 2, your active layer will be layer number 9.
+* If you activate layers 1 then 2, then 3, your active layer will be layer
+  number 3 (because the layer combo `(1,2)` has been activated, but layer 3
+  stacks on top).
+  * deactivate 1: you're on layer 3
+  * deactivate 2: you're on layer 3
+  * deactivate 3: you're on layer 8
+* If you activate layers 3 then 1, then 2, your active layer will be layer
+  number 8. Deativate layer
+  * deactivate any of 1/2/3: you're on layer 0
+
+
+## Fully Working Example code
+
+Below is an example of a fully working keypad that uses combo layers.
+
+```python
+print("Starting")
+
+import board
+
+from kmk.kmk_keyboard import KMKKeyboard
+from kmk.keys import KC
+
+combo_layers = {
+  (1, 2): 3,
+keyboard.modules.append(Layers(combo_layers))
+
+
+keyboard = KMKKeyboard()
+
+
+keyboard.keymap = [
+    [ #Default
+    KC.A,     KC.B  KC.C  KC.D,
+    KC.E,     KC.F  KC.G  KC.H,
+    KC.MO(1), KC.J, KC.K, KC.MO(2),
+    ],
+    [ #Layer 1
+    KC.N1,    KC.N2, KC.N3, KC.N4,
+    KC.N5,    KC.N6, KC.N7, KC.8,
+    KC.MO(1), KC.N9, KC.N0, KC.MO(2),
+    ],
+        [ #Layer 2
+    KC.EXLM,  KC.AT,   KC.HASH, KC.DLR,
+    KC.PERC,  KC.CIRC, KC.AMPR, KC.ASTR,
+    KC.MO(1), KC.LPRN, KC.RPRN, KC.MO(2),
+    ],
+        [ #Layer 3
+    KC.F1,   KC.F2, KC.F3,  KC.F4,
+    KC.F5,   KC.F6, KC.F7,  KC.F8,
+    KC.MO(1) KC.F9, KC.F10, KC.MO(2)
+    ]
+    
+]
+
+if __name__ == '__main__':
+    keyboard.go()
+```

docs/en/layers.md

@@ -33,6 +33,11 @@ Some helpful guidelines to keep in mind as you design your layers:
 - Only reference higher-numbered layers from a given layer
 - Leave keys as `KC.TRNS` in higher layers when they would overlap with a layer-switch
 
+## Using Combo Layers
+Combo Layers allow you to activate a corresponding layer based on the activation of 2 or more other layers.
+The advantage of using Combo layers is that when you release one of the layer keys, it stays on whatever layer is still being held.
+See [combo layers documentation](combolayers.md) for more information on it's function and to see examples.
+
 ### Using Multiple Base Layers
 In some cases, you may want to have more than one base layer (for instance you want to use 
 both QWERTY and Dvorak layouts, or you have a custom gamepad that can switch between 
@@ -40,6 +45,7 @@ different games). In this case, best practice is to have these layers be the low
 defined first in your keymap. These layers are mutually-exclusive, so treat changing default 
 layers with `KC.DF()` the same way that you would treat using `KC.TO()`
 
+
 ## Example Code
 For our example, let's take a simple 3x3 macropad with two layers as follows: