Fixed broken CRC algorithm in sync fast serial to actually detect errors in any byte.
Eliminate USE_CRC from shell.s, since it was never optional.
Eliminate SERIAL_NOWAIT, since it only affects sync serial, and hardly affects it.
Make 57600 serial work with data on 017 D0, D1, D2, or D4, rather than only on D0. Other speeds still require D0.
Move functions between nrpcc.c and nrpcc_core.c and minor tweaks.
Prep for read primitive: use Y for indexing.
Prep for read primitive: smaller serial_write routines (unfortunately slows sync version slightly).
Add serial_read_inl for commands to get 6 extra cycles between bytes.
Add read primitive, greatly reducing overhead for reading memory/port.