Vendor json-ld crate

[clehner]

Vendor the json-ld crate dependency using a git submodule, to enable publish to crates.io.

Progress for #136

Fixes #90

Includes #140, to get CI to work (Closes #140)

Cargo dependencies using git repo URLs cannot be used for publishing to crates.io (unless also including a registry version for publishing). We are depending on the json-ld crate with changes which are not yet published to crates.io. Without being able to depend on this two crates on crates.io, we must either fork and publish it to crates.io under a different name, or vendor it somehow. I wasn't able to get cargo vendor to work, and I'm not sure if that can be used (source replacement) with publishing to crates.io anyway. Instead, the approach taken here is to modify the package to make it work in ssi's workspace. It seems to be working to use a git submodule rather than having to include the repos' source files directly. The json-ld repos is forked and added to git submodules. The changes to json-ld are in the following PR, proposing to use a branch vendor for our fork: https://github.com/spruceid/json-ld/pull/1

• cargo publish --dry-run works

[clehner]

Updated Notice file and Changelog

[wyc]

NOTICE update lgtm!

[clehner]

Thanks. Rebasing...