Fix errant uint8_t length remaining in the UART module.
Redesign the SD driver to allow complex sequences of SPI exchanges
  (e.g. one command followed by several responses, or two-part
  ACMD commands).
Remove the internal EventBus from SdInterface.
Rename Event to event_t. Value types should be named lowercase, reference types uppercase.
Rename SdCommand to sd_command_t.
Implement SD_(GetSector|PutSector) and associated command flows.
Begin scanning the partition table, boot sector, and root directory entries.