planned_features is a view of where the keybrd project is headed.

Top priority
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* Beta testing
* Add breadboard keyboard schematics to tutorials

Medium priority
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* Add matrix-to-layout mapping array (to decouple key matrix from layout)
* Add tutorial_4b_split_keyboard_with_shift_registers

Low priority
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* Add MCP23S18 I/O expander with Serial Peripheral Interface (SPI)