Added unit tests for add/minus multiple words
Added MACROs to pass __FILE__,__LINE__ to functions that can fail; Added fast bit MACROs

1) Added fast MACROs:
  bit_array_get(BIT_ARRAY *arr, bit_index_t i)
  bit_array_set(BIT_ARRAY *arr, bit_index_t i)
  bit_array_clear(BIT_ARRAY *arr, bit_index_t i)
  bit_array_toggle(BIT_ARRAY *arr, bit_index_t i)

2) Moved BIT_ARRAY struct to header

3) Added MACROs for all functions that can fail, to print calling file&line if
   an out-of-bounds error occurs