Function binarySearch

This function does Binary search for `x` in `i`-th row from `j_low` to * `j_high`. * @param mat 2D matrix to search within * @param i row to search in * @param j_low start column index * @param j_high end column index * @param x value to search for * @return column where `x` was found * @return -1 if value not found */