Issue #371 Implemented RtCollaborators methods and unit Tests.
PDD definition fix in RtCollaborators.
RtCollaborators constructor made non public.
Merge branch 'master' of https://github.com/jcabi/jcabi-github into 371
Merge branch 'master' of https://github.com/jcabi/jcabi-github into 371
Issue #371 Impl. Fix for hardcoded User instantiation
Merge pull request #526 from andrescandal/371

#526: pull request Issue #371 Implemented RtCollaborators methods and unit Tests.