Split whitespace before romanize the text

[wannaphong]

From PyThaiNLP/pythainlp-corpus#26, I think pythainlp.transliterate.romanize should split whitespace before romanize the text. It can improve romanize funtion.

[pavaris-pm]

From PyThaiNLP/pythainlp-corpus#26, I think pythainlp.transliterate.romanize should split whitespace before romanize the text. It can improve romanize funtion.

@wannaphong I can help figure out on this krub.

[wannaphong]

Done #924