Implemented #543: better typings for `toJS`
Implemented #543: better typings for `toJS`

andykog/mobservable,andykog/mobx,mobxjs/mobx,mobxjs/mobx,andykog/mobx,mobxjs/mobx,andykog/mobservable,mweststrate/MOBservable,mobxjs/mobx,mweststrate/MOBservable,mweststrate/MOBservable