add perPage optional arg to IssueService.listByRepo
add perPage optional arg to IssueService.listByRepo

kasperpeulen/github.dart,marcojakob/github.dart,kasperpeulen/github.dart,kasperpeulen/github.dart,marcojakob/github.dart,kasperpeulen/github.dart,marcojakob/github.dart,marcojakob/github.dart