Draft: Documentation overhaul for 1.0

• Move docs into dedicated docs/ directory.
• Extend / rewrite docs.
• Use mkdocs to quickly turn markdown files in docs/ into a website and publish that using gitlab pages for now.
  • Timo suggested mdbook, but that needs more config, so for now I'll stick with mkdocs which should not get in the way too much.

This will need proof-reading from people who worked on the actual code, as I am not sure if what I wrote really matches what Conduit is actually doing.

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• I agree to release my code and all other changes of this MR under the Apache-2.0 license