Port to ivoatex#22

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glemson wants to merge 10 commits intomasterfrom

port-to-ivoatex

Commits on Apr 21, 2021

preparing for ivoatex
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Commits on May 9, 2021

Commits on May 10, 2021

Included text from Omar's PR, ported to latex
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fixing some references and moving code listings to appendix. TBD what to do with VO-DSL.
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