Docs in Markdown with Myst and change tutorials to Jupytext notebooks

[basnijholt]

Description

This converts the documentation to Markdown format and uses a new modern theme.

Checklist

• Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• pytest passed

Type of change

Check relevant option(s).

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• (Code) style fix or documentation update
• This change requires a documentation update

[codecov-commenter]

Codecov Report

Merging #355 (f050e01) into master (8b40bf2) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #355      +/-   ##
==========================================
+ Coverage   80.73%   80.75%   +0.01%     
==========================================
  Files          38       38              
  Lines        5071     5071              
  Branches      948      948              
==========================================
+ Hits         4094     4095       +1     
  Misses        833      833              
+ Partials      144      143       -1     

Impacted Files	Coverage Δ
adaptive/learner/average_learner1D.py	78.81% <ø> (+0.37%)	⬆️

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