enh - added bip32 seed parsing

[moocowmoo]

This patch allows the creation of bip38 keys for addresses created by
Richard Kiss' BIP32 pycoin (genwallet) utility.

test vector outputs:

    $ python -c 'import binascii; open("master-private-key-entropy", "w+b").write(binascii.unhexlify("000102030405060708090a0b0c0d0e0f"))' > test.bip3

    $ genwallet -f test.bip32.seed -i
    xprv9s21ZrQH143K3LhEXZMXowo9hkNiaiDVhfvnGpXCimZtiRc5gJmq1YLKjLeg7iR2xDU8gks56oB1JXxwBzNkX5GHQtnjActTpWudHkpbgNu
    main network
    private key
    secret exponent: 64984153768961157829826368741579665624823626924420053033036842588453764406980
    public pair x:   68560981314052299508403304659895617070088830480209293291335193415198847031373
    public pair y:   90409367661552839451235119846362341380971283312313541569547197748756276715666
    tree depth:      0
    fingerprint:     a4ea9e94
    parent f'print:  00000000
    child index:     0
    chain code:      80bbda1ee5fdc3d94a217325d2fd7290cbd69cb91fc69dc8d21e84c9a7fe870d
    WIF:             L22zGSFr75Cix3h8BUKxfyRUTpxEnNC442pvjnwP2F2GNEppUKuc
      uncompressed:  5JuZTcBAK9CigCwQNrh6N4io6dEshdyRi1sHFgQecdFnd7eMcgL
    Bitcoin address: 1G2zt786BsvKJXAvTamW3Bds64e6pcQBMx
      uncompressed:  1PqxhQ4mJNUVUPoWGznMhqf33HGcfaonaH

tested with above values:

    copy secret exponent, paste seed into PyBrainwallet
            64984153768961157829826368741579665624823626924420053033036842588453764406980

    check bip32 checkbox, uncompressed key and address will appear
            5JuZTcBAK9CigCwQNrh6N4io6dEshdyRi1sHFgQecdFnd7eMcgL
            1PqxhQ4mJNUVUPoWGznMhqf33HGcfaonaH

    check bip38 checkbox, encrypt with string 'secret', get bip38 key
            6PRSKsniRtueuhY2LM47EvXtfzKkAbrtsDasXhUpZgNBRqBdy56cHVLCMj

    import key using mycelium wallet, enter password 'secret'

    key successfully imported

[moocowmoo]

error in commit message. should be:

python -c 'import binascii; open("test.bip32.seed", "w+b").write(binascii.unhexlify("000102030405060708090a0b0c0d0e0f"))'

[nomorecoin]

I'll look this over when I have a bit more time set aside.