Make sure the right file gets downloaded when several files per release are published

[aivarannamaa]

Currently minipip only handles the case of single tar.gz file without setup.py in it (ie upip-packages) on its own. All other cases get delegated to pip.

There can be cases, when package publisher wants to provide different content for different targets. For example, most dependencies and content Adafruit-Blinka currently are not relevant for MicroPython.

I don't know whether someone has already used this approach, but according to PEP 425, the most natural thing to do is using separate wheels with micropython or circuitpython Python tag: https://www.python.org/dev/peps/pep-0425/#python-tag . Here is an experiment with this https://github.com/aivarannamaa/packaging_experiment.

If the communities accept this approach, then make sure minipip supports it.