Fix mkdocs build

[kjaffel]

Hi,

We have an error when building mkdocs related to the Sequence import from the collections module in Python: see here.
In Python >= 3.10, Sequence and other abstract base classes (ABCs) were moved from collections to collections.abc.
To fix this issue, I updated Pieter code : https://github.com/kjaffel/mkdocs-doxygen-plugin.
So requirements.txt now point to my fork instead, in order to pick up these changes.

[kjaffel]

git clone [email protected]:cp3-llbb/cp3-llbb.github.io.git 
git fetch origin pull/7/head:branch_name
git checkout branch_name
pip install git+https://github.com/kjaffel/mkdocs-doxygen-plugin.git
pip install mkdocs-markdownextradata-plugin 
mkdocs serve 

This will build the documentation and serve it locally at http://127.0.0.1:8000/, where you can review it.