fix: 优化使用pt工具时注释导致alter子句解析失败的问题

[hanchuanchuan]

添加对各种ALTER语法格式的支持
例如:

-- 这是一条注释
alter table t1 add column c2 varchar(20) comment '!@#$%^&*()_+[]{}\\|;:",.<>/?';

alter table t1 add column `c5` varchar(20) comment \"!@#$%^&*()_+[]{}\\|;:',.<>/?\";  -- 测试注释

[codecov]

Codecov Report

Merging #164 into master will decrease coverage by 0.0121%.
The diff coverage is 0.0000%.

@@               Coverage Diff                @@
##             master       #164        +/-   ##
================================================
- Coverage   58.7680%   58.7558%   -0.0122%     
================================================
  Files           371        371                
  Lines         83462      83464         +2     
================================================
- Hits          49049      49040         -9     
- Misses        30150      30159         +9     
- Partials       4263       4265         +2