Added simplify to MultExpression
Merge Shared_Pointers

Conflicts:
	src/MultExpression.cpp
	src/MultExpression.h
	src/SumExpression.cpp
	src/SumExpression.h
Started on add function for MultExp
Added to add(), multiply() of MultExpression
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
Merge pull request #7 from kylelin47/Shared_Pointers

Shared pointers