These files show the best way to create a class in C++. The class declaration is given
in the header file (intcell_best.h). This is convenient since any class that wants to use
an IntCell can simply include the header file (incell_best.h).
The class implementation is given in intcell_best.cpp. Since the declaration is separate
from the implementation, we can change the implementation without needing to recompile all
classes that use the IntCell class.
The file intcell_best_tester.cpp tests the functionality of the IntCell class.