Don't hardcode keyword list in emacs mode?

[Blaisorblade]

Maybe that's overengineering, but right now both lists need to be kept in sync — and unlike most usual languages (where this duplication exists and it's OK enough), this keyword list does evolve.

As discussed in Blaisorblade@3d98ef5#commitcomment-9674996:

the emacs mode could ask PTS for the list of keywords. It already asks for the list of languages, so that code could be used as a template.