Spacing LilyPond trill spanners

Consecutive LilyPond trill spanners overlap at the same vertical position. The spanner package in 2.11 fixes this with independent control of left and right padding.

   \new Staff {
     \override TrillSpanner #'bound-details #'right #'padding = #2
     c'4 \startTrillSpan
     c'4 \stopTrillSpan \startTrillSpan
     \revert TrillSpanner #'bound-details #'right
     c'4 \stopTrillSpan \startTrillSpan
     c'4 \stopTrillSpan
}