WIP: BIP 32 (hierarchical deterministic wallets)

An important missing piece of bitcore is hierarchical deterministic wallets as described in BIP32. This is rapidly being adopted by the bitcoin community as the next standard for wallets, and is especially valuable in multisig wallets.

Resources on BIP 32:
* [BIP 32](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki0
* [original deterministic wallet explanation by gregory maxwell](https://bitcointalk.org/index.php?topic=19137.msg239768#msg239768)
* [Deterministic wallets advantages and flaws](http://bitcoinmagazine.com/8396/deterministic-wallets-advantages-flaw/)
* [BIP 32 test vectors](https://en.bitcoin.it/wiki/BIP_0032_TestVectors)
* [A (relatively easy to understand) primer on elliptic curve cryptography](http://arstechnica.com/security/2013/10/a-relatively-easy-to-understand-primer-on-elliptic-curve-cryptography/)