1. Implement all Stack related operations (however, may have potential issues or bugs for stack size relocate).
2. Add simple Unit Test for all of the operations (For Push, Pop and GetTopElem, just allocate less than 4 elements for them, so potential issues or bugs may occurred here.)
3. All operations implemented include: InitStack, DestroyStack, ClearStack, IsStackEmpty, StackLength, GetTopElem, Pop, Push.