sw_link opcode (for linking one key to another key)

[kinwie]

To extend sw_previous opcode feature, a new sw_link opcode can be very useful.
For example case like this :
When a crash cymbal hit, then a tom hit, then a crash choke. Using sw_previous won't make the crash choked because there is a tom in between. So, we need a new opcode to make the crash choked.

sw_link:
Previous linked note value.
The region will play if it matched the sw_link value, which is a linked note that had been played before, not just previously

So, also add 'link' value to sw_vel

Example :

sw_link=49
sw_vel=link