In general the changes are:
1. Peripheral (UART, SPI, ADC, I2C, Timer) IDs start from 1, not zero.
2. Make I2C and SPI require the ID even when there's only one bus.
3. Make I2C and SPI accept 'mode' parameter even though only MASTER
is supported.
The safe boot pin, when pulled high during reset rolls back the
firmware to the "factory" image and skips execution of 'boot.py'
and 'main.py'. This is useful to recover from a crash condition.
The system led is used mostly to signal errors.
I2C objects can be freed by the GC and a __del__ method is provided
in order to de-init the peripheral prior to being garbage collected.
UART objects are now added to a local list and this list is now part
of the VM_STATE.
The port currently implements support for GPIO, RTC, ExtInt and the WiFi
subsystem. A small file system is available in the serial flash. A
bootloader which makes OTA updates possible, is also part of this initial
implementation.
