Lightweight serial routines for the aquastar/dlux programming box

- avoid the arduino HW Serial library.
- implement simple fixed 115200 rate, poll-based read and write routines (still using the serial h/w).
- tricky bit was setting the baud rate to 115200 for atmega8 16mhz. needed to enable U2X double rate and recompute the UBRRH/L.
16000000 / 115200 / 8 - 1 == 16 => UBRRH = 0, UBRRL = 16
- reduced flash space from 7516 to 6448 for a saving of 1068 bytes. i think the limit is 8192-512 = 7680.
oops! need to restore CMakeLists.txt

was disabling alot of builds when debugging the aquastar lightweight serial. restored to previous version.