For example, [`put`]() links to the elvdoc for "put".
Also remove the @cf macro now that implicit targets make it easier to link to
other elvdoc sections.
The elvdocs still use the old format (#elvdoc:fn or #elvdoc:var) for now, but
will be changed to "fn" and "var" forms soon.
Also remove the accidentally committed cmd/mvelvdoc. It has been used to perform
the conversion automatically but is not supposed to be committed.
