Doc: Adjusted CG Policy on @lilypond[] variables

Doc: Adjusted CG Policy on @lilypond[] variables

As a reuslt of work on NR 3.2 Titles and Headers, it was necessary to
define some more explicit requirements for using the variables in the
@lilypond[ ... ] construct. Ssuch as removing staffsize
and page sizes within the actual @lilypond example which only add more noise
to the examples.

Also when the need to show taglines and/or page breaks and footers is required then
\book is needed in the example and this will result in unnecessary white space between top and bottom
of the page. So showing page breaking features or numbering examples becomes
problematic within the documentation.

The new @lilypond[papersize=X] variable allows for explicit page sizing without
the need to include it in the example itself. Allowing for better clarity.

The papersize=X takes variables from the scm/paper.scm else 'a4' is presumed.

Moved existing material to the front of this section so that it makes more sense
and added the new requirements for the various preferred variables.