Extend serve.sh/cmd to pass host address

Useful to be able to do `./bin/serve.sh "" "" 0.0.0.0` to listen on all
network adaptors
Add "multiple" attribute to browse widget

And default to non-multiple upload; that’s enough to enable the ability
to take photos/videos directly on iOS
Fix bugs with selective expandable toc macro
Experiment with slightly bigger body text

Trying to improve readability
Docs updates