Handle IPLD changes proposed by @davidar and @mildred

[daviddias]

There is a long made PR by @davidar in ipfs/specs that was never handled and now the IPLD specs live here. @nicola could you make sure to review the proposed changes and incorporate whatever is needed in the IPLD spec?

Link to the PR - ipfs/specs#111

[daviddias]

Another one, made by @mildred, related with this -- ipfs/specs#116

[Stebalien]

Random note: we should probably use / instead of $ as our special character as it's usually reserved for paths. That is, {'/multibase': "...."}.