Implement missing functions in Repo Releases API
Doc Comments added

Add API URLs to comments

Doc Comment Observable Releases Client

Add API URLs to doc comments

Code Analysis fixes
Impl missing Observable Releases Client methods
Remove null check for Int
Add unit tests for the Releases Client
Add unit tests for Observable Releases client
Merge pull request #344 from alfhenrik/repository-releases-api

Implement missing functions in Repo Releases API