Currently, the definitions already have an anchor tag that allows URLs
with fragment identifiers to locate them, but it is rather inconvenient
to obtain such a URL (so-called "permalink") as it would require finding
the a link to the corresponding item in the Synopsis or elsewhere.  This
commit adds hyperlinks to the definitions themselves, allowing users to
obtain links to them easily.

To preserve the original aesthetics of the definitions, we alter the
color of the link so as to be identical to what it was, except it now
has a hover effect indicating that it is clickable.

Additionally, the anchor now uses the 'id' attribute instead of the
(obsolete) 'name' attribute.

Closes #407