Tidy up graphviz show fn to be more system agnostic. Probably needs Windows more work.
Remove guy stuff (will be an external library)
remove old-school midi example.
Update basic MIDI example walkthrough with latest MIDI API
Use correct keyword whey testing for type of midi poly player and also return the player when creating one.

Fixes #259.
Add amp and out-bus params to thx synth and convert it to a defsynth
rather than a definst
remove superfluous dub step call
Update examples