Refactor glissando commands

[trevorbaca]

• Raise exception on attempt to attach glissando to tied not. LilyPond allows c'4 \glissando ~ c'4 but refuses to draw the glissando.

DISCOVERY: \override NoteColumn.glissando-skip = ##t causes LilyPond to create only a single glissando segment. This means that intervening \glissando commands along the course of multisegment glissando are unnecessary (and confusing). This also means that individual "segments" of the glissando can no longer be tweaked (because such "segments" no longer actually exist). This also means that the entire glissando can be tweaked at, say,bound-details.right.padding: use abjad.tweak(2).bound_details__right__padding INSTEAD OF (abjad.tweak(2).bound_details__right__padding, -1). Leads to at least the following:

• Teach abjad.glissando() to omit intervening \glissando commands when stems=True (that is, when \override NoteColumn.glissando-skip = ##t.