* Switch to ES6 imports
* Add attributes and length
* Various improvements + add more tests
- Fix destroy()
- Fix detach()
- Fix map()
- Add NotFoundError, NoRowsUpdatedError and NoRowsDeletedError on Model
* serialize() and toJSON() should return Object/Object[] instead of any
* Fix map()
* More tests taken from Bookshelf website + various fixes
- Fix Bookshelf.transaction return type
- Add id attribute on ModelBase
- Improve ModelBase.parse()
- Fix Model.query()
- Add a constructor to CollectionBase
- Fix CollectionBase.map()
- Fix Collection.attach()
- Fix Collection.query()
- Add Collection.EmptyError
- Fix LoadOptions and FetchOptions withRelated
* No need to specify Knex.QueryBuilder
* toJSON(): Object/Object[] is too restrictive, revert back to any/any[]
* Model.through() returns R, Collection.through() returns Collection<R>
