Make startrack integration backward compatible

Author: bhavesh-hirani

src/Auspost.php

@@ -32,13 +32,24 @@ class Auspost {
 	 * @param string $account_number The AusPost Account number
 	 * @param bool $test_mode Whether to use test mode or not
 	 */
-	public function __construct($api_key, $api_password, $account_number, $star_track = false, $test_mode = false) {
+	public function __construct($api_key, $api_password, $account_number, $test_mode = false) {
 		$this->api_key = $api_key;
 		$this->api_password = $api_password;
-		$this->star_track = $star_track;
-		$this->account_number = !$star_track ? str_pad($account_number, 10, '0', STR_PAD_LEFT) : $account_number; // Ensure the account number is zero padded 10 digits
+		$this->account_number = str_pad($account_number, 10, '0', STR_PAD_LEFT); // Ensure the account number is zero padded 10 digits
 		$this->test_mode = $test_mode;
 	}
+	
+	/**
+	 * Flags the Auspost instance as StarTrack
+	 *
+	 * @param string $account_number The StarTrack Account number
+	 * @return void
+	 */
+	public function starTrack($account_number)
+	{
+		$this->star_track = true;
+		$this->account_number = $account_number;
+	}
 
 	/**
 	 * Perform a GetAccounts API call.