In a text file versioning system (a system that takes into account the contents of the file but also
the contents of the file before each change), a file is represented as an object.
Such an object is characterized by its name (String), content (String) and unique id (int) of
object. The content and file name are set when creating the object using a constructor.
The identifier must also be set when creating the object using a mechanism implemented by you and
it must be transparent to the client of a file object (that is, for example, id value not
must be given by the customer through the manufacturer, etc.). Each file also contains a reference in its state
to another file object that represents the previous version of the current file object. When creating
for a file object, it has no previous versions.