Replaced 256 entry CRC8 table with tiny 2x16 entry table

[arjenlentz]

Hi Paul - here's a little contribution, replacing the 256 byte CRC8 lookup table with a 2x16 byte one, thus saving 224 bytes. See http://lentz.com.au/blog/calculating-crc-with-a-tiny-32-entry-lookup-table for details on how it works.

[PaulStoffregen]

thanks!