Add an easy task runner (nox or tox)

[Saransh-cpp]

This can be closed now. The only failing checks from repo-review are -

1. PY007: Supports an easy task runner (nox or tox)

We don't want this as our testing infrastructure is simple enough.

I'm not sure if I agree with this, tox is very simple to set up (not used nox myself). But I agree it is not urgent either way.

Originally posted by @paddyroddy in #187 (comment)

PS: I personally prefer nox because you can sepcify everything in plain Python, but I use both, so no strong opinions.