Improve syntax

[lucaswerkmeister]

Recognizing string literals with regexes is just shitty, and it doesn’t work (try opening Iterable.ceylon – the long doc comment of the class isn’t recognized). Instead, we should probably override syntax-propertize-function. Look into how Python mode does this (/usr/share/emacs/24.5/lisp/progmodes/python.el.gz).

(I’m assigning myself to this issue, but if anyone else wants to take a shot at this, go ahead.)