One can instead lookup __name__ in the modules dict to get the value.

Disable by default, enable in unix port.

With this patch the n_args parameter is changed type from mp_uint_t to
size_t.

This is extension to CPython, it allows to easily produce human-readable
hex dump:

>>> ubinascii.hexlify(b"\xaa\x55\xaa\x55", b" ")
b'aa 55 aa 55'

Drops Thumb2 arch size by 24 bytes.

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

With this patch str/bytes construction is streamlined.  Always use a
vstr to build a str/bytes object.  If the size is known beforehand then
use vstr_init_len to allocate only required memory.  Otherwise use
vstr_init and the vstr will grow as needed.  Then use
mp_obj_new_str_from_vstr to create a str/bytes object using the vstr
memory.

Saves code ROM: 68 bytes on stmhal, 108 bytes on bare-arm, and 336 bytes
on unix x64.

See issue #699.

This is just a clean-up of the code.  Generated code is exactly the
same.