enh - added bip32 seed parsing

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.bip32.seed

    $ 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 into PyBrainwallet seed,
		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