Spoilers and grammar update

Nerdz Grammar
* `[spoiler]`: just like a ~~plan~~ quote, but the first line must start with `>!`; optional spoiler title supported
* `[user]`/`[project]`: the content of these two tags in no more parsed to avoid error if the nickname/project contains characters used for markdown (like `*`, `_` etc.)

Working on whitespaces and new lines preservation has begun, but still work in progress