Add Mecer subdiver (blzr protocol=mecer)

A subdriver covering an idiom similar to the one used by the megatec subdriver, but with these peculiarities:
- if a command/query is rejected or invalid, the UPS will reply '(NAK\r'
- if a command succeeds, the UPS will reply '(ACK\r'
Remove duplicates in the testing struct
Cosmetic changes