Remove m_HoldNote array entirely. Remove 2sAnd3s. Store hold note
durations in the hold head. hold_tail only still exists when InsertHoldTails
is used, to make SM parsing a little easier (may go away). Add helpers
for iterating over ranges while including or excluding adjacent and overlapping
hold notes. Range operations are now [start,end) instead of [start,end].
(probably more details coming to sm-dev soon)
Glenn Maynard
bb7482e722