Simple Upload File Safely: Validate and process uploaded files

This is a simple class to validate and process uploaded files.

It can take the details of a uploaded file and validate it to verify if it has one of the allowed MIME types and its size does not exceed a given limit for its MIME type.

The class can move the uploaded file to a given directory after verifying that it exists, has the necessary write permissions and does not have already a file with the same name.