v0.6.0

Several adjustments and improvements.

• Update dependencies and crypto libraries.
• New protobuf definitions.
• To support non-standard output returned by different methods, the data
  is not processed in anyway and passed down to standard output.

A breaking change introduced was removing the 'proof' element from the
core DID document as per the specification. The proof is still being
generated and verified for all operations and returned when resolving
an identifier.

{
  "document": "...",
  "proof": "..."
}

For more information: w3c/did-core#293