add spdif output

perhaps add your wav-example too ?
todo: update gui

https://forum.pjrc.com/threads/27491-WAV-playback-sounds-distorted?p=62544&viewfull=1#post62544

update gui docs for 1.00 range not 100.0

do not forget - your own addition :-)

Fix JSON syntax

Document sgtl5000

Remove blah blah. Document based on control_sgtl500.h and
control_sgtl500.cpp.
Clarify that only one frequency modifier can be active at one.  Add
suggestions for pop-free ramping as indicated in datasheet.
Re-order function descriptions to group related ones and put in order of
signal flow.

Add #defines to control_sgtl5000.h to make selecting frequency modifier
(such as tone control) easier.

Chorus and flange gui docs

No more bla bla