RFE: Hairpin object support

[ndickson]

The Hairpin.ms User object from Noteworthy gives control over hairpin placement, angle, and spread, but converting them just as regular hairpins would be a big help, too. Bar 70 of WieniawskiViolinConcerto2_3_Cello_2ndViolins.txt gives an example of a one-note crescendo and a two-note decrescendo:

|User|Hairpin.ms|Pos:-8|StartOffsetX:1|EndOffsetX:4
|Note|Dur:4th,Slur|Pos:-2
|User|Hairpin.ms|Pos:-8|Span:2|Type:decresc|StartOffsetX:3
|Note|Dur:4th,Slur|Pos:-1
|Bar
|Note|Dur:8th|Pos:0|Opts:Stem=Up

If you feel like diving into some of the variations, here's an example of one sloping upward a bit (from the Clarinet part in the 1st mov't):

|User|Hairpin.ms|Pos:-11|Span:4|StartOffsetX:0.8|EndOffsetY:1.5
|Chord|Dur:8th|Pos:-1|Opts:Stem=Down,Beam=First|Dur2:Half|Pos2:3
|Note|Dur:8th|Pos:0|Opts:Stem=Down,Beam
|Note|Dur:8th|Pos:2|Opts:Stem=Down,Beam
|Note|Dur:8th|Pos:1|Opts:Stem=Down,Beam=End

and here's two hairpins with a smaller gap and a tremolo on the same note (from the Timpani part in the 1st mov't):

|User|Hairpin.ms|Pos:-8|StartOffsetX:0.6|EndOffsetX:2.6
|User|Hairpin.ms|Pos:-8|StartOffsetX:5|EndOffsetX:7.5|Type:decresc
|User|TremoloSingle.ms|Pos:0|Offset:-0.5
|Note|Dur:Whole|Pos:0

In MusicXML, they seem to call hairpins "wedges".

It looks like there's already some support for the hairpin note options, so the main difference with the Hairpin.ms object, apart from the additional flexibility, is that it only appears before the notes it affects in the Noteworthy text, instead of appearing on each note.