acurl: cURL wrapper to access HTTP and FTP servers

This class is a wrapper around the cURL extension functions to execute requests to access HTTP and FTP servers.

It can perform several types of operations:

- Ping a server of a given URL to check if it is responding as expected
- Send a request to an URL and retrieve headers and content
- Send an authenticated HTTP requests
- Send HTTP POST requests to an URL
- Upload a file through FTP
- Download a file through FTP

The class can also spoof the browser user agent and handle cookies.