Mnemonic whitespace separator deviates from reference implementation

[gz-c]

The use of strings.Fields in splitMnemonicWords allow more than one whitespace character between words.

https://golang.org/pkg/strings/#Fields

Fields splits the string s around each instance of one or more consecutive white space characters, as defined by unicode.IsSpace

The bip39 spec is not explicit about how words are to be separated.

The reference implementation uses a single space for the separator, after normalizing unicode to ascii:

https://github.com/trezor/python-mnemonic/blob/7d23efe34f3dd537996f31dae34f663207dac232/mnemonic/mnemonic.py#L153

[tyler-smith]

Thanks for this report! This should be tightened up in the spec. I think until 2.0 is done with real native multi language support it makes sense to stick to single spaces. I'll change this.