Add ability to include examples in definitions

[ccameron-chromium]

This is from comment 1378 on CD2 of 2094-50.

Using <dd class="example"> in a definition causes validation errors. I believe @simontWork mentioned having this issue as well.

[palemieux]

As far as I know there cannot be examples in definitions:

https://www.iso.org/sites/directives/current/part2/index.xhtml#_idTextAnchor208

[palemieux]

Nevermind, examples are permitted:

https://www.iso.org/sites/directives/current/part2/index.xhtml#_idTextAnchor226

[simontWork]

I notice that there's also a "deprecated" tag in the ISO specification. That would also be useful as some of the definitions in the document I'm working on are moving away from terms that have been in common use but could be taken out of context.

[SteveLLamb]

@simontWork see #398, will be reviewed on next Tues in ST for approval.