update markdown parser for boards and comments to use new URL schema

[plebe1us]

• from p/business-and-finance.eth to >>>/biz/
• from p/business-and-finance.eth/c/commentCid to >>>/biz/commentCid
• also support >>>/boardAddress and >>>/boardAddress/commentCid
• >>commentCid should only load if it refers to a comment belonging to the same board the user is already in, because the user should at least know what board is being linked (since boards are accessible p2p).
• >>shortCid can only work in the thread view, if the comment it refers to belongs to the thread currently being viewed.