Fix up handling of local links a bit, particularly when there are too many conflicting ones.
Switch all the link attributes to data-link-*. Pass data-link-for to getRef.
Change dfnFor to being parsed into a set, split on whitespace.
Handle data-dfn-for='@foo/bar' as 'bar' as well. Make autolinking take 'for' into account.
Improve some warning text in autolinking.