Added Scheme.format_embedded_scheme_value().

The static method formats values as though they were Scheme values embedded in
a LilyPond document.

    3 -> 3
    True -> ##t
    "foo" -> "foo"
    (1, 2, 3) -> #'(1 2 3)

This differs from Scheme.format_scheme_value() in that
format_embedded_scheme_value() knows whether or not to include a leading
octothorp.
Integrated Scheme.format_embedded_scheme_value() in lilypondnametools.
Updated GeneralizedBeam doctests.
Integrated LilyPondGrobOverride in StaffLinesSpanner.