Support company natively

[birkenfeld]

A "native" company backend (i.e. not relying on completion-at-point-functions/company-capf) would be very useful because with capf, company does not cache the candidates.

So while the completion list is displayed, every keypress will call racer again, which is not necessary and can slow down typing a lot.

[leotaku]

Maybe we could use the now largely abandoned company-racer as a base.