Update to multihash dependency to `0.19` and `cid` dependency to `0.11`

[matheus23]

Is there a path forward for libipld to switch to the newer multihash library?

For anyone reading this and interested in updating to multihash version 0.19, you can also switch to ipld-core, but for anyone else looking for a smoother transition, is updating libipld viable?

[vmx]

I've there's a problem with upgrading to ipld-core, please let me know and I'll have a look. The goal for me is to transition everone away from libipld.