added IObservableSearchClient
prepped ObservableSearchClient
added search to IGitHubClient
added url to ApiUrls for consistency
added all seach urls to ApiUrls
fixed comments
ensure params not null

and fixed code analysis issues too
fixed up mono projects
fixed param names on interface
fixed param names
fixed naming for documentation
Merge pull request #273 from hahmed/search-repo-observable

Search repo observable client