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.
