useAppVersionURL parameter to use upload new version URL

Upload version URL for Hockeyapp is defined here:
http://support.hockeyapp.net/kb/api/api-upload-new-versions

The provided boolean parameter will switch betwenn the standard add app URL:
"https://rink.hockeyapp.net/api/2/apps"
and upload version URL:
"https://rink.hockeyapp.net/api/2/apps/IDENTIFIER/app_versions"