Function SplitN 

pub fn SplitN(
    s: impl AsRef<[byte]>,
    sep: impl AsRef<[byte]>,
    n: int,
) -> Vec<Vec<byte>>

SplitN slices s into subslices separated by sep and returns a slice of the subslices between those separators. If sep is empty, SplitN splits after each UTF-8 sequence.

The count determines the number of subslices to return:

n > 0: at most n subslices; the last subslices will be the unsplit remainder.
n == 0: the result is [] (zero subslices)
n < 0: all subslices

zh-cn

用去掉s中出现的sep的方式进行分割，会分割到结尾，并返回生成的所有片段组成的切片（每一个sep都会进行一次切割，即使两个sep相邻，也会进行两次切割）。如果sep为空字符，Split会将s切分成每一个unicode码值一个字符串。参数n决定返回的切片的数目：

n > 0 : 返回的切片最多n个子字符串；最后一个子字符串包含未进行切割的部分。
n == 0: 返回[]
n < 0 : 返回所有的子字符串组成的切片

Example

use gostd_bytes as bytes;
use gostd_builtin::byte;

   assert_eq!(Vec::<Vec<byte>>::new(), bytes::SplitN(",a,b2,c".as_bytes(), ",", 0));
   assert_eq!(vec![",a,b2,c".as_bytes().to_vec()], bytes::SplitN(",a,b2,c".as_bytes(), ",", 1));
   assert_eq!(
       vec!["", "a", "b2", "c"].iter().map(|x|x.as_bytes().to_vec()).collect::<Vec<Vec<byte>>>(),  bytes::SplitN(",a,b2,c".as_bytes(), ",", -1)
   );
   assert_eq!(vec!["", "a,b2,c"].iter().map(|x|x.as_bytes().to_vec()).collect::<Vec<Vec<byte>>>(), bytes::SplitN(",a,b2,c".as_bytes(), ",", 2));
   assert_eq!(vec!["", "a", "b2,c"].iter().map(|x|x.as_bytes().to_vec()).collect::<Vec<Vec<byte>>>(), bytes::SplitN(",a,b2,c".as_bytes(), ",", 3));
   assert_eq!(
       vec!["", "a", "b2", "c"].iter().map(|x|x.as_bytes().to_vec()).collect::<Vec<Vec<byte>>>(),
       bytes::SplitN(",a,b2,c".as_bytes(), ",", 4)
   );
   assert_eq!(
       vec!["", "a", "b2", "c"].iter().map(|x|x.as_bytes().to_vec()).collect::<Vec<Vec<byte>>>(),
       bytes::SplitN(",a,b2,c".as_bytes(), ",", 5)
   );
   assert_eq!(
       vec!["", "a", "b2", "c"].iter().map(|x|x.as_bytes().to_vec()).collect::<Vec<Vec<byte>>>(),
       bytes::SplitN(",a,b2,c".as_bytes(), ",", 10)
   );