[chbot] Chock Fish etc.

[Mark Atherton]

Well done Volker.

The avr-gcc toolchain from Arduino, version 7.3.0 appears to compile for 
the 328PB OK.

However the legacy 'USART_RX_vect' is now called 'USART0_RX_vect'. 
Surprisingly this does not throw an error, it just does not populate the 
vector table correctly.

Also, AVRDUDE does not know about the PB part, so I had to hard-wire 
328P into Makefile.

So, how much grief is maintaining one-more-toolchain just for an 
odd-ball processor - need to think about this.

Did compile some legacy code OK, but did no generate identical binaries 
(which have run-time miles on them).

Interesting mess.

-Mark