now does rescaling on 256base instead of 100; removes a lot of division by a shift right 8

Needs testing!!! Volunteer please come in. 
Benefits of change:
-248 bytes code generated used gcc 4.7.2
-huge performance increase. My measurements:
   simple mix goes down from 2,87msec to 1.93msec
   middle complex mix goes down from 3,37msec to 2,00msec
   complex mix (with phase change) goes down from 6,87msec to 4,18msec

src/menus.h

@@ -37,6 +37,8 @@
 
 #define NO_HI_LEN 25
 
+// RESX range is used for internal calculation; The menu says -100.0 to 100.0; internally it is -1024 to 1024 to allow some optimizations
+#define RESX_SHIFT 10
 #define RESX    1024
 #define RESXu   1024u
 #define RESXul  1024ul