Hold notes with sustain pedal

[asb2m10]

Per @sonoro1234 request for sustain pedal #12

[sonoro1234]

When pedal is pressed a variable records this state (sustain_on).
When noteoff arrives and sustain is on instead of release (with gate=0) the node is added to a free_queue
When sustain pedal is released sustain_on=false and the nodes in the free_queue are released (via gate=0)

When noteon arrives:

if there is not node for this note: do s_new.
if there is already a node present for this note it means that the node was not released (because sustain is on), one of two actions can be done: (the second one would guaranty a new envelope is triggered)

1-not retrig option: instead of creating a new node we just set (/n_set) this node again.

2-retrig option: release this node, clear the free_queue for this node, do s_new

@asb2m10 does it make sense for you?

[asb2m10]

Yes, this should be fairly easy to implement !