Base58 Check rework

[dcousens]

This pull request changes the base58check API, removing the version parameter completely in favour of simply performing the checksum comparison and encoding/decoding the Base58 only.

This has been chosen in favour of some formats such as the export format in BIP32 using 4-byte version constants instead of the traditional 1-byte. This means there is less code duplication in HDNode and overall the remainder of the code stays relatively similar.
It also makes testing remarkably simpler for base58check.

Finally, an additional change that enforces consistent use of the network objects throughout the code base has been applied.

ECPubKey.getAddress() and ECKey.toWIF() now take a network object. This actually simplified the Message signing code a little bit as well.

[coveralls]

Coverage decreased (-0.11%) when pulling 28dc390 on dcousens:base58rework into 63e6cf9 on bitcoinjs:master.

[dcousens]

Travis exploding again on helloblock. Will hopefully be resolved soon.

[weilu]

@dcousens it's not helloblock this time. https://github.com/dcousens/bitcoinjs-lib/blob/base58rework/test/integration/p2sh.js#L41 instead of getAddress(networks.testnet.pubKeyHash) it should be getAddress(networks.testnet)

[dcousens]

Fixed and good to go.

[coveralls]

Coverage decreased (-0.09%) when pulling 4c6385e on dcousens:base58rework into 2c5b9cf on bitcoinjs:master.

[kyledrake]

+1