mbv: now with functioning timer interrupts!

And a few other nice things.
The bootloader now has an embedded wozmon!
If you know its offset, you can jump to it from the app.

mbv/bootloader/bootloader.ld

@@ -1,6 +1,6 @@
 MEMORY
 {
-    BLRAM (rwx) : ORIGIN = 0x00000000, LENGTH = 2048
+    BLRAM (rwx) : ORIGIN = 0x00000000, LENGTH = 0x1000
 }
 
 SECTIONS
@@ -30,5 +30,5 @@ SECTIONS
         __exidx_end = .;
     } > BLRAM
 
-    _initial_stack_pointer = 2048;
+    _initial_stack_pointer = 0x1000;
 }