WIP Switch To mkdocs

[rlizzo]

Motivation and Context

Why is this change required? What problem does it solve?:

better documentation generator.

Does not work at the current moment (unhappy with API plugin for numpy style docstrings).

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Documentation update
• 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 change)

Is this PR ready for review, or a work in progress?

• Ready for review
• Work in progress

How Has This Been Tested?

Put an x in the boxes that apply:

• Current tests cover modifications made
• New tests have been added to the test suite
• Modifications were made to existing tests to support these changes
• Tests may be needed, but they are not included when the PR was proposed
• I don't know. Help!

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have signed (or will sign when prompted) the tensorwork CLA.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #213 into master will decrease coverage by 66.25%.
The diff coverage is 11.43%.

@@             Coverage Diff             @@
##           master     #213       +/-   ##
===========================================
- Coverage   94.97%   28.72%   -66.25%     
===========================================
  Files          97       90        -7     
  Lines       16572    15742      -830     
  Branches     1634     1616       -18     
===========================================
- Hits        15739     4521    -11218     
- Misses        548    10977    +10429     
+ Partials      285      244       -41     

Impacted Files	Coverage Δ
src/hangar/backends/__init__.py	100.00% <ø> (ø)
src/hangar/backends/hdf5_00.py	80.75% <ø> (-11.94%)	⬇️
src/hangar/backends/hdf5_01.py	81.45% <ø> (-8.68%)	⬇️
src/hangar/backends/lmdb_30.py	40.36% <ø> (-46.27%)	⬇️
src/hangar/backends/lmdb_31.py	40.85% <ø> (-45.62%)	⬇️
src/hangar/backends/numpy_10.py	85.23% <ø> (-9.60%)	⬇️
src/hangar/backends/remote_50.py	93.88% <ø> (-2.49%)	⬇️
src/hangar/bulk_importer.py	0.00% <ø> (-78.07%)	⬇️
src/hangar/cli/cli.py	0.00% <0.00%> (-86.42%)	⬇️
src/hangar/columns/column.py	59.76% <ø> (-38.49%)	⬇️
... and 98 more

[alessiamarcolini]

The RTD build is failing because this PR deletes docs/requirements.txt 😅
The point is: what do we need to keep from that requirements file?

[alessiamarcolini]

Now RTD is able to compile the docs but there are no docs here https://hangar-py--213.org.readthedocs.build/en/213/

BTW I just found this paragraph on the mkdocs documentation (https://mkdocs.readthedocs.io/en/stable/user-guide/deploying-your-docs/#read-the-docs):

To benefit from all of the features offered by Read the Docs, you will need to use the Read the Docs theme which ships with MkDocs. The various themes which may be referenced in Read the Docs' documentation are Sphinx specific themes and will not work with MkDocs.

What do we do know?