`anchor.extract(string, anchor)` will find and extract a zettel anchor
from any string passed in.
It can be given an optional anchor regex which will supersede any regex
set in the plugin options.
By choosing 'line' in the `zettel_link_following` option, the link to be
opened will be searched for on the complete rest of the line, meaning
from the cursor to the newline symbol onwards.
`g:zettel_link_following` can be set to `cursor` or `line` to change the
way zk detect the closest link to follow to (or create a new link for).
Setting it to `cursor` will look for the current word under the cursor and
decide if it is a followable link. `line` will look from the current
cursor position to the end of the line instead.
