Build - further automate windows build process

Still more work to be done here!

Doc - fix mistake in midi out docs

FX - add experimental guitar saw synth

Will potentially be used as a base for future pitch-detection-style synths/FX

GUI - fix version number displayed in info window

changelog - update release date for v2.11

Changelog - minor final tweaks

GUI - update version string in doc

Merge pull request sonic-pi-net#810 from jweather/win28

use Sonic Pi's ruby to build docs in win-build-app.bat

GUI - disable experimental arg completion

GUI - save restore geometry