Effect can be easily achieved by ubinsacii.hexlify(hash.digest()).

This drops the size of unicode_isxdigit from 0x1e + 0x02 filler to
0x14 bytes (so net code reduction of 12 bytes) and will make
unicode_is_xdigit perform slightly faster.

This also pulls out hex_digit from py/lexer.c and makes unichar_hex_digit

This allows using (almost) the same code for printing floats everywhere,
removes the dependency on sprintf and uses just snprintf and
applies an msvc-specific fix for snprintf in a single place so
nan/inf are now printed correctly.

Fixes sign-compare warning.

ISO C forbids conversion between function pointers and void*, gcc
-pedantic triggers a warning.

Background: trying to make an amalgamation of all the code gave some
errors with redefined types and inconsistent use of static.

Can be enabled by defining MICROPY_PORT_WLAN_URN=1 in mpconfigport.h.

When entering the interrupt handler of a given GPIO port, more than
one pin could have pending interrupts, therefore care must be taken
to service each interrupt one by one before leaving.

This reverts commit 8fbabab1. Turned to
cause problems on MacOSX.

Addresses issue #1255.

With newer versions of esp_iot_sdk the iram1_0_seg started to overflow.
Now it doesn't.

Addresses issue #1254.

Moved modesp.o to flash and increased size of the irom0_0_seg segment. The new
value was taken from NodeMCU linker script.