Support for LV ties

[rpatters1]

I'm wondering about the best way to support LV ties in the api. Would it make sense to add isTieLetRing to NoteData? It would have somehow be exclusive with isTieStart, if only by convention. (That is, only one could be set.)

Another approach would be to add an API-level enum for tie starts that had 2 values (TieStart::regular, TieStart::letRing). But this would be a breaking change.

[rpatters1]

This may need to be more comprehensive. After researching the recommendation of how to handle ties in musicxml, we are going to need some control over tie and tied, or at least model the possible scenarios.

For example, a tie end on a second ending is supposed to be modeled

 <notations>
    <tied type="start"/>
    <tied type="stop"/>
  </notations>

with no <tie>. Note the order above. Presumably if tie continued at the start of the 2nd ending to the next note, there would be a third element of <tied type="start"/>.

Maybe this is all old hat to you, lol. I've been avoiding the musicxml mess up till now, focusing instead on mnx. (Which hallelujah is json.)