[DOC] Improve documentation rendering

[qbarthelemy]

Types of changes

Correct equations, references, bullet points, etc rendering in documentation.
No code modification.

Motivation and context / Related issue

There are many mistakes in the current documentation https://pythonot.github.io/

How has this been tested (if it applies)

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.06%. Comparing base (39cd6ec) to head (950daac).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #710   +/-   ##
=======================================
  Coverage   97.06%   97.06%           
=======================================
  Files          98       98           
  Lines       19955    19955           
=======================================
  Hits        19370    19370           
  Misses        585      585