new plugin to integrate Algolia in Pelican

[srault95]

https://github.com/srault95/pelican-algolia-search

Sorry for the documentation in French but if a volunteer want to take care of it, I would replace the readme with pleasure.

[kdeldycke]

This mono-repository no longer accept any submission of Pelican plugin as submodules. Instead, new plugin should be packaged as independent modules so you'll be free to publish them out on PyPi.

To help, there a plugin template available at: https://github.com/getpelican/cookiecutter-pelican-plugin