split_str includes the splitter substring, conflicting with the documentation

[owenthewizard]

Each element yielded is guaranteed not to include the splitter substring.

use bstr::ByteSlice;

fn main() {
    let my_str = b"Hello ";
    let mut iter = my_str.split_str(b" ");
    assert_eq!(iter.next(), Some(b"Hello".as_ref()));
    assert_eq!(iter.next(), None);
}

thread 'main' panicked at src/main.rs:7:5:
assertion `left == right` failed
  left: Some([])
 right: None