Reboot nc-time-axis

[bjlittle]

📰 Custom Issue

Breath some life back into nc-time-axis.

To-do checklist:

• Enable GH discussions
  • Create Releases GH discussions category
  • Create 1.3.0 release discussion
• Add Issue templates
• Add PR template
• Create 1.3.0 release milestone
• Create 1.3.0 project board
• Update labels
• Configure repo settings
  • Allow squash merging only
  • Require conversation resolution before merging
  • Require linear history
• Migrate CI from travis-ci to cirrus-ci
  • Linux container testing for py37, py38, py39, coverage only for py39
  • Add linting CI for black, flake8, and isort
• Adopt black
• Adopt flake8
• Adopt isort
• Adopt setuptools-scm and drop versioneer
• Adopt pre-commit
• Migrate setup.py to setup.cfg
• Rationalise package dependencies for conda and PyPI
• Adopt pytest
• README.rst to README.md
• Add badges
  • will add cirrus-ci, codecov and pre-commit post merge in separate pr
• Drop Python2
  • Decide on the minimum Python3 version
    • Going with py37, py38, and py39