Deprecating the fret-diagram markup in favor of fret-diagram-terse and fret-diagram-verbose

[Carl D. Sorensen]

Now that the fretboard context is relatively mature, I believe the
fret-diagram markup is no longer needed.

As a reminder, the fret-diagram markup allows the user to specify a number
of characteristics in the markup definition string, such as the number of
strings, the number of frets, the size, etc.  These same characteristics can
be set by the fret-diagram-details property of TextScript for markups and of
FretBoard for FretBoards.

I believe that it makes the best sense to separate the presentation from the
content.  The content for a fret diagram is a series of (string, fret,
finger triplets).  We have the fret-diagram-terse interface, which allows
the specification of (string, fret, finger) triplets in a compact,
easy-to-type, and easy-to-read form.  We also have the fret-diagram-verbose
interface, which has the (string, fret, finger) triplets as Scheme lists and
hence is very convenient for program creation.

I'd like to deprecate the fret-diagram interface, as it is no longer needed
for its original use and is cluttering up the code.

What is the process by which we deprecate syntax?

Thanks,

Carl