add warning for .feature addrsize, clean up switch in SetFeature

src/ca65/pseudo.c

@@ -1043,6 +1043,12 @@ static void DoFeature (void)
             ErrorSkip ("Invalid feature: '%m%p'", &CurTok.SVal);
             return;
         }
+
+        if (Feature == FEAT_ADDRSIZE) {
+            /* Warn for depreciated .feature addrsize */
+            Warning (1, "Depreciated feature: '.feature addrsize'. Pseudo function .addrsize is always available.");
+        }
+
         NextTok ();
 
         /* Optional +/- or ON/OFF */