Provide showing of usage ref and ptr in class fields.
Move creation of pointers to separate directory.
Rename History.h to HistoryOfSubscript.h and move code.
Move creation of references to separate file.
Move using of ref and ptr in classes to separate file.
Move check on polymorphism and code with UB to separate class.
Move example of once initializing references to separate file.
Move example on input const ref to separate file.
Include iostream in files where it needs.

Remove including from main.cpp.
Update code of HistoryOfSubscript.h and add comments.
Add comments to creation of pointers and references.
Add comments to code with UB.
Add coments to single init of reference.
Add comments to code which use refs and ptrs in classes.
Add comments to code which shows polymorphism with refs and ptrs.
Make order of function calls in main as in article.