Add support for milestones (#62)

Added support for the [Milestone](https://developer.github.com/v3/issues/milestones/) API's for GitHub Issues.

GitHubComments.ps1

@@ -29,10 +29,10 @@ function Get-GitHubComment
         Issue number to get comments for. If not supplied, will return back all comments for this repository.
 
     .PARAMETER Sort
-        How to sort the results, either created or updated. Default: created
+        How to sort the results.
 
     .PARAMETER Direction
-        How to list the results, either asc or desc. Ignored without the sort parameter.
+        How to list the results. Ignored without the sort parameter.
 
     .PARAMETER Since
         Only comments updated at or after this time are returned.
@@ -117,6 +117,8 @@ function Get-GitHubComment
     $elements = Resolve-RepositoryElements
     $OwnerName = $elements.ownerName
     $RepositoryName = $elements.repositoryName
+    $uriFragment = [String]::Empty
+    $description = [String]::Empty
 
     if ($null -ne $Since)
     {