renamed QSE_AWK_EXTRAKWS to QSE_AWK_NEXTOFILE

fixed a minor glitch in qse_pio_t
fixed the nil field to xnil in qse_rbt_t to minimize collision with external header files since nil is a commonly found macro
added a simple optimization to qse_memcpy()

qse/include/qse/cmn/rbt.h

@@ -226,7 +226,7 @@ struct qse_rbt_t
 
 	qse_byte_t       scale[2];  /**< length scale */
 
-	qse_rbt_pair_t   nil;       /**< internal nil node */
+	qse_rbt_pair_t   xnil;      /**< internal nil node */
 
 	qse_size_t       size;      /**< number of pairs */
 	qse_rbt_pair_t*  root;      /**< root pair */