refactor: add `momery.js` file
refactor: `Relation` constructor
refactor: add `BaseModel` into `KnexModel` obj

and read version from `package.json`
add: `getModel` method to `utils.js` file

支持在定义关系的时候, `model` 字段用 `Model` 对象或 `Model` 的名字
add: utils test
chore: update to `0.0.6`