Change the arguments of `cfb_invert_area`, `cfb_print`, and
`cfb_draw_(point|line|rect|circle)`, which used unsigned integers to
specify coordinates to signed integers.
This is because coordinate are usually specify with real numbers,
so it is difficult to use unless negative numbers are accepted.
We clip drawings outside the drawable area on the implementation side.
Accordingly, we will update the API version to 0.10.0.
Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>
a0f37226d5