[yoshimi-user] Multiple Jack outputs patch for yoshimi

[Дерябин А. <and...@gm...>]

Hi, all!

     I'm resending my patch - It's working for me for 2 weeks already - 
no crashes or artifacts.

Jeremy, please include this patch in current git version or reject it if 
you think it is useless, so I'll should not wait and resending it again. 
Thanks :).

Here is the summary of changes:

1. Add separate jack stereo output for every configured yoshimi 
instrument channel (chX_l, chX_r).
2. Rename previous outl, outl channels into mix_l, mir_r to reflect 
changes in yoshimi structure. Though, these channels act like the old 
ones - mix outputs from all channels with system efx (sends and inserts) 
applied.
3. System, effects are applied only form mixed outputs due to their 
stereo nature. It's not a problem. because separate channels can be 
routed to external production program like ardour where different number 
of effects can be used.