Classe Upload: Validate and handle uploaded files

This class can be used to validate and handle files uploaded via Web forms. It can check:

- If the file does not exceed a given size limit
- If the file name has one of the accepted extensions
- If there is a file with the same name in the target directory

If the uploaded file verifies the validation rules, the class moves the file to a given directory.

The class may also return the URL for a link to download the uploaded files.

The code and the comments are in Italian.

In Italian:

Classe Upload è una classe con semplici funzioni da usare per uppare i file.

Contiene le funzioni di: sovrascrivi rinomina File, estensioni consentite, dimensioni massime, restituzione link al file uppato.