Embedded Public Key IDs

[btoms20]

What:

• This PR adds additional support for PeerIDs with embedded public keys in their ID.

Changes:

• The PeerID equality check can now compare across traditional (SHA256) and Embedded PubKey (Identity) IDs.
• Introduced public func traditionalB58String() throws -> String to force the traditional SHA256 version of the ID.
• The existing CID initializers support embedded public key ID's now.
• PeerID stores the actual Multihash instead of just the Multihash's underlying value.

Fixes:

#11

Result:

Allows the following

// Embedded Public Key
let peerID1 = try PeerID(cid: "12D3KooWAfPDpPRRRBrmqy9is2zjU5srQ4hKuZitiGmh4NTTpS2d")
// Traditional (SHA256 variant)
let peerID2 = try PeerID(cid: "QmPoHmYtUt8BU9eiwMYdBfT6rooBnna5fdAZHUaZASGQY8")

// Equality Check
print(peerID1 == peerID2)  // true

// Embedded version has a public key available (for signature verification, etc)
print(peerID1.type)  // .isPublic

// Traditional version does not have a public key (it's an ID only)
print(peerID2.type)  // .idOnly

// Embedded PeerID's
// default to staying embedded
print(peerID1.b58String)  // 12D3KooWAfPDpPRRRBrmqy9is2zjU5srQ4hKuZitiGmh4NTTpS2d

// but we can still grab the traditional SHA256 value if necessary
print(peerID1.traditionalB58String())  // QmPoHmYtUt8BU9eiwMYdBfT6rooBnna5fdAZHUaZASGQY8

// Traditional PeerIDs
// can only ever be traditional (since hashes are one way streets)
print(peerID2.b58String)  // QmPoHmYtUt8BU9eiwMYdBfT6rooBnna5fdAZHUaZASGQY8

print(peerID2.traditionalB58String())  // QmPoHmYtUt8BU9eiwMYdBfT6rooBnna5fdAZHUaZASGQY8