add spoiler tag support for comments

Given the popularity of movie/tv talk on the site already we might need it soon.

Allowing something similar to the old mouseover method we used on reddit in the olds days could work as a stopgap until a more fleshed out feature can be developed, e.g. [SPOILER]("this is the spoiler") ... Currently to get that to work you need to have it as [SPOILER](http:// "this is the spoiler") so removing the http:// requirement would be nice.