[Feature]: support for Python 3.9+

[jesteria]

What would you like the software to do?

I would like nPrintML to work with as little set-up as possible.

As operating systems increasingly ship with default versions of Python greater than 3.8, more users will be inconvenienced by nPrintML's lack of support for these. Moreover, it is ideal for nPrintML to support whichever is Python's most recent stable version, for the convenience of users who do install Python themselves.

Existing workarounds

I can install a version of Python that nPrintML supports. (In theory anyway.)

Implementation notes

This work appears to depend on #66. AutoGluon v0.1.0 does not support Python v3.9+. (Moreover, only "pre-release" versions of AutoGluon suggest support for Python v3.9+. As such, this issue might currently be blocked.)

[jesteria]

The now-latest version of autogluon – 0.6.0 – supports Python versions 3.7-3.9.