In light of #302 I think we must tighten vcsh up a lot.

https://gist.github.com/EvgenyOrekhov/5c1418f4710558b5d6717d9e69c6e929 & https://jmmv.dev/2018/03/shell-readability-strict-mode.html largely agree but I don't know off-hand if either form is adopted more widely. I would prefer the more verbose set -o form for readability. @mirabilos what would you suggest?