chenged a bit directory structure
2ndboot.c : removed last blocking bug !
  the button callback did not check that a write was ongoing,
  so the file was reopened while being written, causing rewriting of the beginning
  of the file to the flash (this bug was hard to trace ! )


audio.h : fixed strange noise (off by one buffer size)
flashit.c : a few error checks, comments
linker_loader.ld : discarded some extra stack unwinding attributes, dont know why they were there
bitbox.h : removed reference to audio_frame which should be private
  bitbox_main : added the extern here
bitbox.mk : added a linker_raw reference
test_kernel : simplified a reference
encode_anim: removed

Signed-off-by: Makapuf <makapuf2@gmail.com>