RE: Interline spacing for multiple lines of lyrics

[Charles Collins]

With thanks to Mats Bengtsson:

The following gets the individual lines of lyric text closer to each other
vertically than they are by default. Essentially it is setting the line
leading in staff space units.

\paper {
    \translator {
        \LyricsContext
        minimumVerticalExtent = #'(-0.75 . 0.75)
        }
} 

But it was also necessary to deal with the space between the staff and the
uppermost line of the lyrics text (which is in this case below the staff). 

    % Eliminate preconceived notions about the size of the staff.
    \set Staff.minimumVerticalExtent = #'(0 . 0)

    % Set spacing below staff explicitly.
    \set Staff.extraVerticalExtent = #'(-1 . 0)

The preceding extraVerticalExtent setting works nicely for the staff with
the bass clef. To get the same effect for the staff with the treble_8 clef,
it was necessary to use:

    \set Staff.extraVerticalExtent = #'(1 . 0)

which lets the lyrics move upward, compensating for the space occupied by
the little 8 below the clef, which apparently forms part of the staff space.

Maybe it would be nicer to do this with extra-offset on the whole lyric
block, but the method here captures the idea of forcing the staff space to
be smaller than it thinks it should be -- as the treble_8 clef has
aggressively expanded the vertical size of the entire staff box, rather than
just peeking discreetly out below the box there safely in clef territory.