[Meta] New spoiler tags for comments!

We didn't have real spoiler tags for comments yet, so I added them ([taken from r/asoiaf](https://www.reddit.com/r/asoiaf/comments/i2mg6/attention_we_now_have_a_new_spoilertagging_system/)). Here's how it works:

If you write a spoiler like this:

[Secret!](/spoiler "Vaan is actually an Archadian spy")

it will show up as:

Secret!

Normal, non-spoiler links can still be used like this:

[Google](https://google.com)

And will show up like this:

Google