Note deprecated fields in HTML and Markdown outputs

[jacobtolar]

This updates the Markdown and HTML outputs to prefix field descriptions with Deprecated. if the field is configured with [deprecated=true].

While there is a table at the end listing all the fields by option (at least in the HTML output), it's probably more helpful to see them in context.

[jacobtolar]

Ping someone on the PR (Lots of people, including myself, won't get a notification unless pinged directly)

Oops, I missed this item.

@pseudomuto - please take a look; thanks!

[pseudomuto]

Hey there, thanks for the PR!

There are two things I think should be done before merging this:

1. Add the deprecated notification to the DocBook template as well
2. Add an entry to the CHANGELOG.md file

Once added we'll get this merged

[jacobtolar]

Will address your three suggestions. Thanks!

[pseudomuto]

This LGTM 👍

Let's just address the version bump and contributing file points and get this merged!