Refactor documentation

[yakky]

Description

Refactor documentation to improve:

• maintainability by keeping documentation and code in the same place
• clarity by rewording
• depth by exposing api autodoc

Temporarely targeted to #621 for easier review, to be rebased after #621 is merged

References

Fix #622

Checklist

• [x] I have read the contribution guide
• [x] Code lint checked via inv lint
• [x] changes file included (see docs)
• [x] Usage documentation added in case of new features
• [ ] Tests added

[codecov[bot]]

Codecov Report

Merging #623 into develop will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #623   +/-   ##
========================================
  Coverage    94.14%   94.14%           
========================================
  Files           22       22           
  Lines         1041     1041           
  Branches       137      137           
========================================
  Hits           980      980           
  Misses          23       23           
  Partials        38       38           

Flag	Coverage Δ
#unittests	94.14% <0.00%> (ø)

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[coveralls]

Coverage increased (+0.1%) to 96.74% when pulling 15a82a14ea2209eacb74a30efa11e43279b49b8e on feature/issue-622-improve-documentation into 7e9536b0165d8e394386f1952d7878061c90a8db on feature/issue-620-admin-customization.