Compilation error with fresh build depending on didkit 0.3.0

[cobward]

Building a crate that depends on didkit 0.3.0 will fail for fresh builds (no Cargo.lock). This can be replicated by creating a new crate which only depends on didkit 0.3.0 and running cargo build.

This is due to didkit 0.3.0 depending on ssi 0.3.0 and did_methods of the form "x.y". Did method crates increment z when ssi is upgraded, so both ssi v0.4.0 and v0.3.0 are in the dependency tree of didkit.

I suggest:

• We release didkit v0.3.1 and yank v0.3.0.
• Going forwards in didkit we always depend on did method versions of the form x.y.z to prevent ssi version clashes.