Added updateWhere, updateById, and deleteWhere

- `updateWhere(query: JsObject, fields: JsObject)` allows you to update all models that match
  the query (see mongodb query API), updating the fields according to the mongodb update object
  API
- `updateById(id: ID, fields: JsObject)` allows you to update the model
  with the specified `id` with the fields according to the mongodb
  update object API
- `deleteWhere(query: JsObject)` deletes all models that match the query
  object according to the mongodb query API