CI upgrades

[ConorMacBride]

• Add flake8 config
• Add isort config
• Add doctest to tox
• Fix existing failures
• Add both to Azure Pipelines
• Add a test that was missing
• Add a CITATION.cff file

[codecov]

Codecov Report

Merging #46 (da957d2) into main (762f21c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #46   +/-   ##
=======================================
  Coverage   95.05%   95.05%           
=======================================
  Files          18       18           
  Lines        1376     1376           
=======================================
  Hits         1308     1308           
  Misses         68       68           

Impacted Files	Coverage Δ
src/mcalf/models/results.py	100.00% <ø> (ø)
src/mcalf/profiles/gaussian.py	100.00% <ø> (ø)
src/mcalf/utils/mask.py	100.00% <ø> (ø)
src/mcalf/models/__init__.py	100.00% <100.00%> (ø)
src/mcalf/models/base.py	84.87% <100.00%> (ø)
src/mcalf/models/ibis.py	91.97% <100.00%> (ø)
src/mcalf/profiles/voigt.py	96.84% <100.00%> (ø)
src/mcalf/utils/collections.py	100.00% <100.00%> (ø)
src/mcalf/utils/misc.py	99.22% <100.00%> (ø)
src/mcalf/utils/plot.py	100.00% <100.00%> (ø)
... and 7 more

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