早期版本（2.0 之前）使用rules 进行数据校验处理，2.0 之后进行了修改使用
validators，这样更加明确
参考格式
addpost {
// if any rule returns false,
// SQLer will return 422 code, with invalid rules.
//
// $input is a global variable holds all request inputs,
// including the http headers too (prefixed with `http_`)
// all http header keys are normalized to be in this form
// `http_x_header_example`, `http_authorization` ... etc in lower case.
validators {
post_title_length = "$input.post_title && $input.post_title.trim().length > 0"
post_content_length = "$input.post_content && $input.post_content.length > 0"
post_user = "$input.post_user"
}
bind {
title = "$input.post_title"
content = "$input.post_content"
user_id = "$input.post_user"
}
exec = <<SQL
INSERT INTO posts(user_id, title, content) VALUES(:user_id, :title, :content);
SELECT * FROM posts WHERE id = LAST_INSERT_ID();
SQL
}