Updated pyproject.toml and deleted files that are no longer necessary

[eurunuela]

Closes #60.

This PR changes:

• Only use pyproject.toml for installation, dependencies, etc.
• Removes files that are no longer necessary.
• Makes Python 3.8 the minimum version.
• Makes scikit-learn 1.2 the minimum version.
• Updates the tests from 3.5-3.7 to 3.8-3.10.
• Creates __about__.py.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -4.48% ⚠️

Comparison is base (556d013) 95.43% compared to head (e95b78a) 90.96%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
- Coverage   95.43%   90.96%   -4.48%     
==========================================
  Files           3        3              
  Lines         307      310       +3     
  Branches        0       32      +32     
==========================================
- Hits          293      282      -11     
  Misses         14       14              
- Partials        0       14      +14     

Files Changed	Coverage Δ
mapca/mapca.py	89.63% <ø> (-5.70%)	⬇️
mapca/__about__.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[tsalo]

I haven't tested anything, but the changes look good to me.