In this PR, we introduce TOKENIZE function for inverted index, it is used as following:
```
SELECT TOKENIZE('I love my country', 'english');
```
It has two arguments, first is text which has to be tokenized, the second is parser type which can be **english**, **chinese** or **unicode**.
It also can be used with existing table, like this:
```
mysql> SELECT TOKENIZE(c,"chinese") FROM chinese_analyzer_test;
+---------------------------------------+
| tokenize(`c`, 'chinese') |
+---------------------------------------+
| ["来到", "北京", "清华大学"] |
| ["我爱你", "中国"] |
| ["人民", "得到", "更", "实惠"] |
+---------------------------------------+
```
