Added Remember-Token to Authenticate

Renamed Authenticate to Authenticate2 and added remember-me support
Created Authenticate as wrapper for Authenticate2 for backwards
compat.

api.go

@@ -15,6 +15,7 @@ const (
 type TastytradeAPI struct {
 	httpClient *http.Client
 	authToken  string
+	remToken   string
 	host       string
 }