mini-mwc and cppm fixes

mini-mwc
- updated pin mappings in comment block.
- CMakeLists.txt to use pro5v328 for mini-mwc (atmega328p instead of atmega168p).
- use defined(__AVR_ATmega328P__) instead of defined(__AVR_ATmega328__).

cppm
- handle more than 8 channels in cppm stream.
- store only the first 8 channels though.