Usage:

    import machine
    wdt = machine.WDT(0, 5000) # 5 second timeout
    wdt.feed()

Thanks to Moritz for the initial implementation.

APA102 is a new "smart LED", similar to WS2812 aka "Neopixel".

Move definition of mp_builtin_open_obj to a separate module, then file.c
becomes more or less compartmentalized FatFs file class, which can be used
together with file class implementations for other (V)FSes.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.