Drop support for Python 3.7

[simonjayhawkins]

from https://numpy.org/neps/nep-0029-deprecation_policy.html

On Dec 26, 2021 drop support for Python 3.7 (initially released on Jun 27, 2018)

The next release after 1.3 can be scheduled for 6 months, and we can drop 3.7 support in the next release.

[simonjayhawkins]

updated the 2.0 milestone date to match.

[Anupam-USP]

Hey, can I take this issue? I found this article that I think will be useful?

[simonjayhawkins]

We won't be starting this until 1.3.0rc0 is released at the earliest, since we don't have a separate branch for the release after next.