Fixes#167
For Serial when selecting TinyUSB. Can't include in the core because Arduino IDE
will not link in libraries called from the core. Instead, add the header to all
the standard libraries in the hope it will still catch some user cases where they
use these libraries.
See https://github.com/earlephilhower/arduino-pico/issues/167#issuecomment-848622174
Update pico-sdk to 1.1.2
Add methods to block the opposite core while doing flash updates.
Ensure opposite core is stopped in LittleFS and EEPROM while doing
flash updates.
Update documentation with new calls.
