Mapping for nullbits tidbit board with bit-c pro (KMKfw#916)

Adds nullbits tidbit board and bitc promicro mapping

boards/nullbitsco/README.md

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+Mappings for [nullbits](https://nullbits.co/) keyboards,
+often based on the [BIT-C pro micro MCU](https://nullbits.co/bit-c/).

boards/nullbitsco/tidbit/README.md

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+Keyboard mapping for the [nullbits tidbit](https://nullbits.co/tidbit/).
+
+Copy `kb.py` and `main.py` to your top level circuitpython folder beside the kmk folder.
+Edit the key mapping in `main.py` to match your build,
+for example the number and location of encoders and double-size keys.
+
+The Keyboard constructor supports a couple of optional arguments (see `kb.py`).
+
+If you're setting your tidbit up in landscape mode, 
+with the USB connector at top right instead of top left, pass 
+`landscape_layout=True`.
+
+You can specify the active encoder positions by passing a list like
+`active_encoders=[0, 2]` which corresponds to the 1st and 3rd positions shown
+in [step 6](https://github.com/nullbitsco/docs/blob/main/tidbit/build_guide_en.md#6-optional-solder-rotary-encoder-led-matrix-andor-oled-display) of the build guide.
+The default is for a single encoder in either of the top two locations labeled 1 
+in the build diagram, i.e. `active_encoders=[0]`.  Pass an empty list if you skipped
+adding any encoders.
+
+You can control the RGB backlights with the [RGB extension](http://kmkfw.io/docs/rgb).
+Here's an example:
+
+```python
+from kb import KMKKeyboard
+from kmk.extensions.rgb import RGB, AnimationModes
+
+keyboard = KMKKeyboard(active_encoders=[0], landscape_layout=True)
+
+rgb = RGB(
+    pixel_pin=keyboard.pixel_pin, 
+    num_pixels=8,
+    animation_mode=AnimationModes.BREATHING,
+    animation_speed=3,
+    breathe_center=2,
+)
+keyboard.extensions.append(rgb)
+
+```

boards/nullbitsco/tidbit/kb.py

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+import board
+
+from kmk.kmk_keyboard import KMKKeyboard as _KMKKeyboard
+from kmk.modules.encoder import EncoderHandler
+from kmk.quickpin.pro_micro.bitc_promicro import pinout as pins
+from kmk.scanners import DiodeOrientation
+
+encoder_pinout = [
+    (pins[13],  pins[14],   None),      # enc 0, button mapped in matrix
+    (pins[10],  pins[11],   None),      # enc 1 (optional)
+    (pins[5],   pins[4],    None),      # enc 2 (optional)
+    (pins[0],   pins[1],    None),      # enc 3 (optional)
+]
+
+
+class KMKKeyboard(_KMKKeyboard):
+    '''
+    Create a nullbits tidbit keyboard.
+    optional constructor arguments:
+
+    active_encoders=[0, 2] to list installed encoder positions (first=0)
+        then declare keyboard.encoders.map = [(KC.<left> , KC.<right>, None), (...)]
+    landscape_layout=True to orient USB port top right rather than left (default)
+    '''
+#    led = digitalio.DigitalInOut(board.D21)
+#    led.direction = digitalio.Direction.OUTPUT
+#    led.value = False
+    row_pins = (
+        pins[15],
+        pins[9],
+        pins[8],
+        pins[7],
+        pins[6],
+    )
+    col_pins = (
+        pins[19],
+        pins[18],
+        pins[17],
+        pins[16],
+    )
+    pixel_pin = pins[12]
+    diode_orientation = DiodeOrientation.ROW2COL
+    i2c = board.I2C  #TODO ??
+
+    def __init__(self, active_encoders=[0], landscape_layout=False):
+        super().__init__()
+
+        if landscape_layout:
+            self.coord_mapping = [
+                row * len(self.col_pins) + col
+                for col in range(len(self.col_pins))
+                for row in reversed(range(len(self.row_pins)))
+            ]
+
+        if active_encoders:
+            self.encoders = EncoderHandler()
+            self.encoders.pins = tuple([encoder_pinout[i] for i in active_encoders])
+            self.modules.append(self.encoders)

boards/nullbitsco/tidbit/main.py

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+from kb import KMKKeyboard
+
+from kmk.keys import KC
+
+# add active_encoders=[0, 2] to constructor if first and third encoders installed
+keyboard = KMKKeyboard()
+
+XXXXX = KC.NO
+
+keyboard.keymap = [
+    [
+        XXXXX,  KC.PSLS, KC.PAST, KC.PMNS,
+        KC.P7,  KC.P8,   KC.P9,   KC.PPLS,
+        KC.P4,  KC.P5,   KC.P6,   KC.PPLS,
+        KC.P1,  KC.P2,   KC.P3,   KC.PENT,
+        KC.P0,  KC.P0,   KC.PDOT, KC.PENT,
+    ]
+]
+
+if __name__ == '__main__':
+    keyboard.go()

kmk/quickpin/pro_micro/bitc_promicro.py

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+import board
+
+# Bit-C-Pro RP2040 pinout for reference, see https://nullbits.co/bit-c-pro/
+# (unused)
+pinout = [
+    board.D0,  # Enc 3
+    board.D1,  # Enc 3
+    None,  # GND
+    None,  # GND
+    board.D2,  # Enc 2
+    board.D3,  # Enc 2
+    board.D4,  # Row 4 + breakout SDA
+    board.D5,  # Row 3 + breakout SCL
+    board.D6,  # Row 2
+    board.D7,  # Row 1
+    board.D8,  # Enc 1
+    board.D9,  # Enc 1
+    # Unconnected breakout pins D11, D12, GND, D13, D14
+    board.D21,  # WS2812 LEDs labeled D10/GP21 but only board.D21 is defined
+    board.D23,  # MOSI - Enc 0
+    board.D20,  # MISO - Enc 0
+    board.D22,  # SCK - Row 0
+    board.D26,  # A0 - Col 3
+    board.D27,  # A1 - Col 2
+    board.D28,  # A2 - Col 1
+    board.D29,  # A3 - Col 0
+    None,  # 3.3v
+    None,  # RST
+    None,  # GND
+    None,  # RAW
+]
+# also defined: board.LED_RED, board.LED_GREEN, and board.LED_BLUE == board.LED