Member FLUSH_ON_EVERY_DEBUG_STATEMENT: I should probably use Streams instead of Prints, so Espressif boards can flush as well.
Member IncrementButton::State: Add states for initial press.
Member IncrementDecrementButtons::State: Add states for initial press.
Class KV_Builder: LoggerMathTypes.hpp
Class MAX7219: Wiring diagram for SPI connection.
Member MAX7219::update () override: Does this really have to happen on each update?
Class MAX7219_Base: Wiring diagram for SPI connection.
Member MAX7219_Base::init (): Rename to begin.
Member MAX7219SevenSegmentDisplay::display (const uint8_t(&characters)[N], uint8_t startPos=0): Find out what this function does, and write documentation.
Member MAX7219SevenSegmentDisplay::printHex (uint8_t digit, uint8_t value): Rename to printHexChar and create function that actually prints longer hexadecimal numbers.