fix latex docs

[rfindler]

This adjusts the documentation to build in latex mode.

I'm not completely sure if the renaming I did to change youtube-embed to youtubeembed is kosher. The html still looks okay to me, tho. I did that change because latex macro names cannot have hyphens in them, apparently.

[rfindler]

Oh, and you can test it out with either raco setup --doc-pdf or just scribble --dest x --latex gui-easy.scrbl. After the latter, you'd also need to do cd x ; pdflatex gui-easy to see the error in the version without this commit.

[Bogdanp]

Thanks!