Division algorithms implementation

[mgorzkowski]

There are lots of operations already implemented, but still, there are no division algorithms implemented.
It should be done similarly to the abn_mul algorithm.

Prototypes are:
void abn_div(abn_t *result, abn_t *arg_a, abn_t *arg_b); - for division one abn_t by another abn_t (unsigned)
void abn_divu(abn_t *result, abn_t *arg_a, abn_unit value); - for division one abn_t by abn_unit
void abn_sdiv(abn_t *result, abn_t *arg_a, abn_t *arg_b); - for division one abn_t by another abn_t (signed)

Implementation should be placed in src/operations/multiplicative.c
Prototypes should be placed in include/abn.h

There are also some tests to write. Look at the test directory.