Fix typo: Said "projects," Dragon wrote "objects"
Enable supercollider package for slideshows

Incredibly, I was defining the listings style properly, but not specifying
it in the options for individual listings!
Add printhead bits for sclang-prettifier, but don't use them yet

sclang-prettifier is not compatible with fontspec yet.
https://bitbucket.org/Jubobs/sclang-prettifier/issue/1