Bugs to fix:
-  A few key hits ignored after leaving the application  (could not reproduce)
-  Lost keyboard control at startup                      (could not reproduce)

Simple improvements:
-  demo:	Try 284x124 at (-60, -28) (all disadvantages)
-  display:	Rectangle-based drawing functions
-  tales:	Test all font encodings
-  time:	Compute CLOCKS_PER_SEC
-  core:	Add VBR handlers debugging information (if possible)
Larger improvements:
-  errno:       Introduce errno and use it more or less everywhere
-  bopti:	Monochrome bitmaps blending modes
-  bopti:	Handle partial transparency
-  core:	Implement all callbacks and a complete user API
Other whole modules:
-  Serial communication through 3-pin
-  USB communication
-  Sound playback and synthesizing (if possible)
-  Overclock (relaunch clocks when overclocking)

Things to investigate:
-  Packed bit fields alignment
-  Registers that may need to be saved within setjmp()
-  Registers that may need to be saved and restored by gint
-  Possible bug when optimizing __attribute__((interrupt_handler))

Configuration:
-  ATEXIT_MAX (16)
-  RTC_CB_ARRAY_SIZE (5)
-  EVENTS_QUEUE_SIZE (64)
-  GINT_NO_SYSCALLS (undefined)