simplify creation of Serial1

[ladyada]

since Serial is hardcoded for debug, its nice to use one of the extra uarts for talkin' to a GPS

this diff:
adafruit@1bf6318
makes it easier, just add HardwareSerial Serial1(2); and in setup: Serial1.begin(115200);

note that uart #1 is not available because it is shared with SPI flash, so it was not tested. uart #2 works great on gpio #16 + #17. no other gpio's are available

[me-no-dev]

I'm totally cool with this :) You want to PR the change, or do you want me to add it together with shiftIn/Out stuff? Also if flash is DIO, UART1 should be available.

[me-no-dev]

added here thanks!