GitLab

- Don't use gpp anymore, all preprocessing uses pandoc lua filters api
   * No more MD vs md and no intermediate files
   * panda.lua + others
   * custom lua script to replace svg with pdf when the backend is Latex
   * TODO: something is broken when using svgs with docx
      * TODO: maybe go back to pngs for docx
- update reveal.js
   * simple white theme
   * TODO: customize the theme, add logo...
- update css, options,