add support mysql and use pymysql . all test local

[golangpkg]

增加了个 type 类型，可以区分 mysql 和 postgres 了。

其他参数都可以支持，就是看 ID 是否可以替换成：

default=lambda: uuid.uuid4() 这样就可以兼容 mysql 和 PG 了。本地测试一些创建功能是没有问题的。

[crazywoola]

Please add my wechat: crazyphage

[takatost]

Based on our communication, here's the summary:

1. We hope that other developers don't need to worry about the differences in the underlying database when declaring Model class and writing migrations. Every developers use the same set of conventions.
2. If there's a need for pure SQL execute, se compatible syntax as much as possible.
3. If there are some PgSQL-specific syntax in codes, it may be necessary to modify the codes to support different databases.

[quicksandznzn]

+1

[kaktos]

+1

[takatost]

Sorry, but due to the lack of response for a long time and MySQL not being in our roadmap, this PR will be closed.

[simplast]

+1