decide what to do about peerDependencies

[zkat]

I really don't particularly want to support peerDependencies if I can get away with it, but the truth is they're out there in the wild and we probably still need to support them in some capacity.

We should come up with a plan to move forward with, in concert with #171, which is what a lot of people use peerDeps for.

The current situation out in the wild is a bit annoying:

1. NPM 1, 2, and >7 automatically install peerDependencies and error on incompatibility
2. NPM 3-6 warns about missing or incompatible peerDeps
3. pnPM installs them into a fancy folder structure
4. Yarn v1-3 just warns about them like NPM 3-6 does.