Whitespace in input mnemonic produces different seed

[lrettig]

The BIP39 spec doesn't say anything about how to handle whitespace. The library we're using, https://github.com/tyler-smith/go-bip39, does different things with whitespace depending on how you use it. We should probably ignore all whitespace and split the mnemonic into a list of words before turning it into a seed. We currently trim whitespace at the beginning and end of the mnemonic but not intermediate whitespace.

[lrettig]

Fixed in #59. We're not the first to get bitten by this, see:

iov-one/weave#923
iov-one/weave@fd82cc9#diff-6569bb577f21a71b8e731cb7dc0f2b24R96
tyler-smith/go-bip39#29