Add collapsable answers

[SouthKoreaLN]

Is your feature request related to a problem? Please describe.
Nothing important, nothing frustrating. Just thought that if I want to keep posting puzzles like this one, it'd be nice to have a way to collapse an answer to hide spoilers. But then again, unlikely this will ever be the primary use of SN, so I won't care much if it does not get implemented :)

Describe the solution you'd like
Something like what is illustrated here: https://gist.github.com/pierrejoubert73/902cc94d79424356a8d20be2b382e1ab

Describe alternatives you've considered
Alternative: just ask people not to look at the answers before replying.