JSON column type

The JSON type was introduced in MySQL 5.7.8. Inserting values as string works fine, but selecting from the table returns this error:

```
--- FAIL: TestStorage (0.09s)
    storage_test.go:32: Unknown FieldType 245
```

I tried casting the JSON column to VARCHAR in the select but soon find out MySQL doesn't support it. Is there a workaround for dealing with JSON columns? Thanks!
