Update multihash dependency and Blockstore interface

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Updates to completely new API of multihash
• Update function name which generates Cid from cbor encoded bytes
  • Cid::from_bytes() is kinda misleading as it insinuates it is just deserializing a Cid, when it is in fact generating a new one
• Updates blockstore put to pass in the hash type to allow using other hash types for Cid generation (needed by Erlich)

Reference issue to close (if applicable)

Closes

Other information and links

[ec2]

thanks for this