[#77728418] add Subscrition#topics to return associated topic objects
[#77728418] spec for subscription > topic cumulative totals
[#77728418] get subscriptions endpoint spec
[#77728418] the subscription endpoint with age_of_oldest_message
[#77728418] catch nil message
[#77728418] refactored the way in which topics are derived from a subscription
[#77728418] stop flakey spec by ordering results
[#77728418] PR comments addressed
[#77728418] corrected bad spec and nested Array
Merge pull request #26 from HouseTrip/platform/implement-monitoring-endpoints-get-subscriptions-77728418

Platform: Implement monitoring endpoints - GET subscriptions [#77728418]