Hits Counter: Keep track of file download counts

This class can be used to keep track of the number of times a file is download from a site.

It handles the request to serve the file contents with the appropriate HTTP headers. It supports resuming partially downloaded files.

The file download counters are stored in files that are read and updated once a file served by the class is fully downloaded.

The class can generate download links and present the current download count for a given file.