Added second and third priorities

Author: WyriHaximus

src/Priority.php

@@ -4,9 +4,13 @@
 
 final class Priority
 {
-    const FIRST   = 1000;
-    const EARLY   = 750;
-    const DEFAULT = 500;
-    const LATE    = 250;
-    const LAST    = 0;
+    const FIRST       = 1000;
+    const SECOND      = 999;
+    const THIRD       = 999;
+    const EARLY       = 750;
+    const DEFAULT     = 500;
+    const LATE        = 250;
+    const THIRD_LAST  = 2;
+    const SECOND_LAST = 1;
+    const LAST        = 0;
 }