rxjs-all-subjects-private addition

Wrote a rule rxjs-all-subjects-private to enforce that the access level modifier of subjects which are class properties to be private, based off the rxjs-finnish rule.

e.g.

class Mock {
  public propertySubject$ = new Rx.Subject<any>();
         ~~~~~~~~~~~~~~~~     [Subject 'propertySubject$' must be private.]
}

Would this be something of interest to integrate?

[cartant]

Sure. If you want to open a PR, that would be great. Please be sure to include some tests, though.

[cartant]

If you want you could consider renaming the rule (again … sorry) to something like rxjs-no-exposed-subjects?