These allow to fine-tune the compiler to select whether it optimises
tuple assignments of the form a, b = c, d and a, b, c = d, e, f.
Sensible defaults are provided.

This allows to use the On-Chip retention registers for both the
RTC and to share notification flags between the bootloader and the
application. The two flags being shared right now are the "safe boot"
request and the WDT reset cause. we still have 2 more bits free for
future use.

These changes also help reduce the hibernate wake-up time to 1s.

Addresses issue #1154.

This allows to test options passed to cmdline executable, as well as the
behaviour of the REPL.

The aim here is to improve coverage of the code.

Supports suspend and hibernate modes. Waking is possible throug GPIO
and WLAN.
The mpcallback class is generic and can be reused by other classes.

Also add another method to change the pin's interrupt mode
on the fly.

Such functions are never used after MicroPython has started, and they
remain in RAM wasting space. Now they are placed in a special section
named "boot" which sits just before the heap, allowing us to extend
the effective heap area up to the new boot section. Right now, this
gives us back ~1K, but in the future, more functions might end up in
there as well.