Unlike optimize_upip, which instantiates a separate distutils/setuptools
command to run after "sdist", sdist_upip overrides "sdist" implementation,
so it simplifies publishing workflow (no need to run adhoc commands).
Besides what optimize_upip did (post-porocessing to remove superfluous
files and recompressing with gzip 4K dictionary), sdist_upip also
adds pre-processing step of generation resource module (R.py) from
resource files.
So, now there's a single (and standard) command to generate a distrubution
package for MicroPython.
Paul Sokolovsky