[Extension] showdown-spoiler, support for spoiler tags within markdown

[kvmet]

This extension lets you use double pipes to hide spoilers. They can be revealed by clicking on the hidden section. It has no effect inside of <pre> and <code> sections.

This is a ||spoiler||.

It also can ||spread  
across line breaks||

Link to repo: https://github.com/kvmet/showdown-spoiler