⌂ Aligning the ends of hairpins to NoteColumn directions

The ends of hairpins may be aligned to the LEFT, CENTER or RIGHT of NoteColumn grobs by overriding the property endpoint-alignments, which is a pair of numbers representing the left and right ends of the hairpin. endpoint-alignments are expected to be directions (either -1, 0 or 1). Other values will be transformed with a warning. The right end of a hairpin terminating at a rest is not affected, always ending at the left edge of the rest.