Added bitcoin-base58 library.
Use base58Check instead of base62.
New ID format: OT-[base58Check with version byte 0].
Renamed functions s.t. they do not mention base62 anymore.

Also fixed up some comments that are not accurate anymore.
Use the (ripemd160 . sha256) hash algorithm for identifiers.
Merge pull request #348 from benma/base58

New ID format: OT-(base58Check encoded)