[issue #2] remove compiler warning for typedef'ed generic compare function and its specific implementation

[bonitoflakez]

Issue generated in #2 was due to a combination of missing declarations and incorrect function pointer assignments.

Error Identification: We encountered an error indicating an incompatible pointer type when initializing compare_item_func_list.

Understanding Error: Error message pointed to the compare_item_func_list initialization, suggesting an issue with the compare_person function pointer.

• Declaration of compare_item_func_list: We found that compare_item_func_list was not correctly declared. To address this, we defined compare_item_func_t as a function pointer type.

• Declaration of compare_person: We noticed that the compare_person function was missing its declaration. We added the declaration of compare_person before the compare_person_wrapper function.

• Modification of Wrapper Function: We modified the compare_person_wrapper function to have the correct signature and included the call to the compare_person function.

• Definition of compare_person: Finally, we added the implementation of the compare_person function based on the desired comparison criteria.