addFriend(steamID, callback) {
		return StdLib.Promises.timeoutCallbackPromise(10000, ['personaName'], callback, true, (resolve, reject) => {
			this._send(EMsg.ClientAddFriend, {steamid_to_add: Helpers.steamID(steamID).getSteamID64()}, (body) => {
				if (body.eresult != EResult.OK) {
					return reject(Helpers.eresultError(body.eresult));
				}

				resolve({
					personaName: body.persona_name_added
				});
			});
		});
	}
Send (or accept) a friend invitiation.
@param {(SteamID|string)} steamID - Either a SteamID object of the user to add, or a string which can parse into one.
@param {function} [callback] - Optional. Called with `err` and `name` parameters on completion.