Update SmartInteger.cpp

Added divide method
Merge Shared_Pointers

Conflicts:
	src/SmartInteger.cpp
	src/SumExpression.cpp
	src/SumExpression.h
Added simplify to MultExpression
Started on add function for MultExp
Added to add(), multiply() of MultExpression
Merge branch 'Shared_Pointers' of https://github.com/kylelin47/COP-Project into Shared_Pointers

Conflicts:
	src/SumExpression.cpp