update ignore file; return -1 when array is empty
array has only 1 element, return 0 if the element is found.
return correct postion when target is at the mid of array
return correct position when target is at the left half of mid
remove duplicated code
update the findInLeftHalf to findInHalf
return correct position when target is at right side of mid
add test: return correct position when getting target in array; return -1 when target is NOT in array