Package publishing should check semver compat #128

The wit-component crate provides a function semver_check for checking that two packages are semver compatible.

The publish path should fetch any packages that are in the same semver series, and then check to make sure the to-be-published package is semver compatible with them.

We could allow disabling this check with an optional --no-verify flag for exceptional situations, but I believe this behavior should be enforced by default.