Percussion and Piano tweaks

Piano no longer aliases due to Pulse Sine. As a result, it's now a
pseudo 4-op. I may change this back to 2-op but, I really like how it
sounds.

Fixed percussion issues - now I'm satisfied with the hi-hats and
cymbals.

Guiros added. Completely forgot about them.

Vibra slap now sounds better.

Revamped solo string instruments, and removed Pulse Sine weirdness from
them.

Various tweaks here and there to volumes.