Big diff, but it’s mostly just whitespace changes; ignore whitespace and
it’s much smaller, though still not as tiny as it could potentially be.
Essentially, this just duplicates everything for the hashbrown variant.
It’d be possible to use generic associated types to achieve this without
the duplication, but that depends on currently-unstable features, and is
probably slightly more painful to use anyway. I’ll keep the approach in
mind for a possible version 2, but for now this is the pragmatic route.
I’m quite pleased with how this has turned out.
Given the stability-despite-instability of hashbrown (that the API
surface we’re depending on hasn’t changed since 0.1.1), and the
deliberate altered SemVer guarantees for it, it was very tempting
to leave the hashbrown range open, `version = ">=0.1.1"` or at least
`version = ">=0.1.1, <1"`, but for some reason or other I ended up
deciding not to. I’m still of two minds about it, really.
