Smart pointer I, Step 2
-----------------------

Code have been divided into two files, smart_pointer and smart_pointer.cpp. 
Some member functions are still defined "inclass".

Operators for negation (!), equality (==) ineequality olikhet (!=) have been
added.

The operators for equality and inequality are overloaded to compare two smart 
pointers, or a smart pointer and a raw pointer, of corresponding types.