I like the addition of a constant but there's still a couple places in this diff where the url is explicitly used.

This is subjective but I generally dislike trailing slashes in url constants -- it is more semantically 'correct' for the trailing fragment to be an absolute path.  Either way, having to remember the presence/absence of a trailing slash is a problem.

Ways to work around involve changing the setting name:

- `wiki_host = wiki.lesswrong.com`
- `wiki_url_trailing_slash = http://wiki.lesswrong.com/`
- `wiki_url_no_trailing_slash = http://wiki.lesswrong.com/`

My personal choice would be `wiki_host` as it is the most flexible -- it can be used in situations where protocol isn't needed (user-facing text, etc)