GetAuthSessionTicket implementation

[jackma92]

Hey, would You be interested in getting a implementation of SteamUser.GetAuthSessionTicket added here? If so, would You suggest having it as new handler (SteamAuthTicket?), or perhaps tacking the method on to already existing handler, like SteamUser or SteamApps? Even though it's not verified by steam, proper implementation should probably use PublicIP and ServerTime out of SteamUser.LoggedOnCallback, but it also needs Tokens from SteamApps.GameConnectTokensCallback and ability to call SteamApps.GetAppOwnershipTicket. There's also problem when someone tries to call it before receiving GameConnectTokens, since those are needed, but I'm not sure if I should care?

My current implementation can be found here, and I'd love to get it built-in, as I believe it might be useful to some people.