More post parsing

[mushrom]

Backlinks and quotes are already supported, but we'll probably also need

• bbcode, might already be a lib that does this
• automatic link parsing
• dice
• board references (>>>/out/)

etc, we'll most likely want a separate file that does just parsing stuff

[notgne2]

Backlinks we will need:

• >>1 (Thread/Post)
• >>>/a/1 (Thread/Post)
• >>>/a/ (Board)

Make sure to remember that those links can both be links to threads and links to posts, the safest bet is on the backend, parse these post links, resolve them in the database to figure out of they are post or thread links, and provide adequate information to the templates so they can linkify correctly.

We will need redtext< too, not to forget