Overview
We should provide a topic / subject tagging mechanism, through hashtags. Users should generally insert them anywhere in their posts.
Implementation
We already parse out tags for posts. We should store these in a tags table and make tagged posts accessible on users' blogs at write.as/{name}/tags/{tag}.
Known issues
Right now, any hashed part of a URL, especially when pasted or used as a link in Markdown, gets extracted as a tag (issue: {T346})
Design
Tags should be parsed on the server side, and the HTML served with special <span> and <a> tags that make the pound symbol more transparent, but link to the above blog tags URL.