wip: Use PHPDoc for documentation

[recanman]

Documentation is very inconsistent, and PHPDoc is very simple to use and generates nice-looking documentation.

Progress:

• [x] wordsets
• [x] base58
• [ ] Cryptonote
• [ ] daemonRPC
• [ ] ed25519
• [ ] jsonRPCClient (after #138 merge)
• [x] mnemonic
• Serialize
• SHA3
• [x] subaddress
• [x] Varint
• [ ] walletRPC

[recanman]

Closing as merge with refring's code is already documented.