Eliminate data movement.

* Pass pointer to nunchuk structure to access them indirectly
  so we eliminate data movement.
* Sensible parameter naming and remove verbose comments

Memory footprint
----------------
Program:    7824 bytes (23.9% Full)
(.text + .data + .bootloader)

Data:        404 bytes (19.7% Full)
(.data + .bss + .noinit)

src/nto_nunchuk/main.c    | 31 +++++++++++++++----------------
src/nto_nunchuk/nunchuk.c | 25 ++++++++++---------------
src/nto_nunchuk/nunchuk.h |  8 +++-----
3 files changed, 28 insertions(+), 36 deletions(-)