Doc contains broken links

[Boscop]

The doc contains broken links, e.g. the second link on that page for AsChangeset (the first one works).
Maybe others are affected too (depending on the cause).

[beatgammit]

I also noticed that the link to update in IncompleteUpdateStatement is broken as well (I'm guessing it should be update_statement? I think this one is because something was renamed.

[theduke]

I just tested the docs at http://docs.diesel.rs/diesel/index.html with a linkchecker.

It reports no broken links, so I think this can be closed.

[killercup]

Nice. Thanks, @theduke!

We currently cheated this issue by using absolute URLs (well, absolute paths) in a few places. This is good for now, but we should revisit this when a better solution (e.g. rust-lang/rfcs#1946) is available.