Release v0.24 - A Sight For Sore Eyes (#1539)

* Add release notes and bump version to 0.24

* run "build FormatCode" to fix up whitespace/formatting issues

* Fix failing Ssh key tests due to "validation exception".  This key must be in use on github (under another user, most likely from these tests failing).  Changed to a new SSH key and tweaked tests to reduce chance of a key being created and not destroyed

* Assignee and Assignees cant both be specified on NewIssue.  We missed this one in the PR.  Marked Assignee as [Obsolete] and fixed tests to use Assignees

* Fix a couple of Reactions tests that were calling the wrong client methods

* Fix timeline tests - looks like the response class has changed shape a bit, it now has an Issue object in the payload and Id field isnt present (leaving Id field there in case other timeline events do use it)

* Fix some following tests that require the test user to follow more than 1 other user

* Unskip these Event tests now because apparently they work!

* add breaking changes notes

* Update ApiErrorMessageSafe to return null for empty and whitespace strings (#1540)

* return null if ApiError.Message is empty or whitespace

* Uncomment test, which now passes

* update release notes to include PR1540

* Add "Bot" AccountType, was causing a deserialization exception when running the integration test "SearchForExcludedLanguage" (#1541)

* Update to include PR1541

* add bullets to make release notes easier to read

* markup additional code mentions in notes

* Fix grammar

fields => field

Octokit.Reactive/Clients/IObservableReferencesClient.cs

@@ -25,7 +25,7 @@ namespace Octokit.Reactive
         [SuppressMessage("Microsoft.Naming", "CA1716:IdentifiersShouldNotMatchKeywords", MessageId = "Get",
             Justification = "Method makes a network request")]
         IObservable<Reference> Get(string owner, string name, string reference);
-        
+
         /// <summary>
         /// Gets a reference for a given repository by reference name
         /// </summary>