make TapDance a module (#281)

* extract tapdance logic into a module

* clean out old tapdance code

* canonicalize key variable names

* split _process_tap_dance into td_pressed and td_released

* implement consistent argument order

* update documentation

* implement Module.process_key for key interception and modification

* fix tapdance realesing instead of pressing

* fix: default parameters in key handler

* cleanup holdtap

* add error handling to modules process_key

* fix: key released too late

Tapped keys didn't release on a "key released" event, but waited for a
timeout. Resulted in, for example, modifiers applying to keys after the
modifier was released.

* fix lint/formatting

* fix tap_time reference in modtap + minimal documentation

* fix lint

docs/modtap.md

@@ -4,7 +4,10 @@ added to the modules list.
 
 ```python
 from kmk.modules.modtap import ModTap
-keyboard.modules.append(ModTap())
+modtap = ModTap()
+# optional: set a custom tap timeout in ms
+# modtap.tap_time = 300
+keyboard.modules.append(modtap)
 ```
 
 ## Keycodes

docs/modules.md

@@ -13,3 +13,4 @@ put on your keyboard
 when tapped, and modifier when held.
 - [Power](power.md): Power saving features. This is mostly useful when on battery power.
 - [Split](split_keyboards.md): Keyboards split in two. Seems ergonomic!
+- [TapDance](tapdance.md): Different key actions depending on how often it is pressed.

docs/tapdance.md

@@ -23,6 +23,8 @@ keymap somewhere. The only limits on how many keys can go in the sequence are,
 theoretically, the amount of RAM your MCU/board has, and how fast you can mash
 the physical key. Here's your chance to use all that button-mash video game
 experience you've built up over the years.
+[//]: # (The button mashing part has been 'fixed' by a timeout refresh per)
+[//]: # (button press. The comedic sentiment is worth keeping though.)
 
 **NOTE**: Currently our basic tap dance implementation has some limitations that
 are planned to be worked around "eventually", but for now are noteworthy:
@@ -31,16 +33,23 @@ are planned to be worked around "eventually", but for now are noteworthy:
   currently "undefined" at best, and will probably crash your keyboard. For now,
   we strongly recommend avoiding `KC.MO` (or any other layer switch keys that
   use momentary switch behavior - `KC.LM`, `KC.LT`, and `KC.TT`)
+[//]: # (This also doesn't seem to be the case anymore; as long as the layer)
+[//]: # (is transparent to the tap dance key.)
+[//]: # (At least KC.MO is working as intended, other momentary actions haven't)
+[//]: # (been tested.)
 
 Here's an example of all this in action:
 
 ```python
 from kmk.keycodes import KC
-from kmk.macros.simple import send_string
+from kmk.handlers.sequences import send_string
+from kmk.modules.tapdance import TapDance
 
 keyboard = KMKKeyboard()
 
-keyboard.tap_time = 750
+tapdance = TapDance()
+tapdance.tap_time = 750
+keyboard.modules.append(tapdance)
 
 EXAMPLE_TD = KC.TD(
     KC.A,  # Tap once for "a"