updated notations
hashtable.h: added notations
hashtable.cpp: added notations.
customerhashtable.h: updated sigantures and notations.
updated methods and notation.
storehashtable.h: updated signatures and notations
storehashtable.cpp: updated methods and notation.
inventoryhashtable.h: updated signatures and notations.
inventoryhashtable.cpp: updated methods and notation.