Make design implementation independent

[memoz1981]

Hi (Privet).

I watched your youtube video, which is very interesting. Would want to try to implement the heap allocation management using linked list or tree. For this raising this PR to have main heap.h header file and then other implementation specific files.

This would allow anyone to add other implementations of the heap.h.

Please feel free to comment, and I would make the amendments.

Thanks in advance, Mehdi