* Renamed str::split -> str::split_byte
* Renamed str::splitn -> str::splitn_byte
* Renamed str::split_func -> str::split
* Renamed str::split_char -> str::split_char
* Renamed str::split_chars_iter -> str::split_char_iter
* Added u8::is_ascii
* Fixed the behavior of str::split_str, so that it matches split_chars
and split (i.e. ["", "XXX", "YYY", ""] == split_str(".XXX.YYY.", "."))
* Fixed str::split_byte and str::splitn_byte so that they handle
splitting UTF-8 strings on a given UTF-8/ASCII byte and also handle ""
as the others do
