Autocomplete suggestion improvements

[bhollis]

From @nev-r:

autocomplete has no real token recognition, it doesn't know to look as far back as ^, or a colon, or a quote, or "the last completed and valid term". until i can type not forgo and get a suggestion that erases the not, autocomplete is not doing its job well enough imo. certainly it's not doing its job if typing arctic haz suggests arctic "arctic haze". it's very hard to get dim to suggest multi-word things rn because a ton of them start with crappy little filler words like "the" and "a"