Mkdocs conversion

[rozyczko]

Draft PR to expose the issue rather than directly merge.
@AndrewSazonov 's modifications in another branch (new_docs) should be either merged here or the other way around.

This branch is what's currently published on https://easyscience.github.io/corelib/

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.80%. Comparing base (822cba3) to head (90146fb).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #176   +/-   ##
========================================
  Coverage    80.80%   80.80%           
========================================
  Files           52       52           
  Lines         4261     4261           
  Branches       739      739           
========================================
  Hits          3443     3443           
  Misses         633      633           
  Partials       185      185           

Flag	Coverage Δ
unittests	80.80% <ø> (ø)

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Files with missing lines	Coverage Δ
src/easyscience/__init__.py	100.00% <ø> (ø)
src/easyscience/base_classes/__init__.py	100.00% <ø> (ø)
src/easyscience/io/__init__.py	100.00% <ø> (ø)
src/easyscience/models/polynomial.py	100.00% <ø> (ø)
src/easyscience/variable/__init__.py	100.00% <ø> (ø)