Usage of icons in markdown

[aronmolnar]

We could improve our markdown capabilities by introducing an easy syntax for icons. This could be like mkdocs does it, e.g.:

:cloud:
:material-cloud:

(I also like their mkdoc's easy search: https://squidfunk.github.io/mkdocs-material/reference/icons-emojis/?h=icons

The licenses of the following icon sets allow us commercial usage:

• Font Awesome: https://fontawesome.com/v4/ (SIL OFL 1.1)
• Material: https://fonts.google.com/icons (Apache 2.0)
• Octicons https://github.com/primer/octicons (MIT)