Update documentation

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Documentation hasn't been updated, nor re-generated in a long time.

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Transformed tex files from the docs/ directory into markdown, and imported them with some small changes into the wiki. 2b continued...

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Slowly progressing, and updating along the way as I deprecated matrix and rng wrappers which are not actively maintained anymore

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@meyerj informed me that @tdelaet 's home page (and hence the generated docu) is no longer available. To be discussed what's the best way forward here. Probably it makes most sense to integrate the documentation here https://docs.orocos.org/bfl/overview.html

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See also orocos/orocos-docs#16 (small note: orocos docs is using rst iso markdown, but convertors seem to exist)