Added mention of FTP proxies

PROXY

 Get an ftp file using a proxy named my-proxy that uses port 888:

 curl supports both HTTP and SOCKS proxy servers, with optional authentication.

 It does not have special support for FTP proxy servers since there are no

 standards for those, but it can still be made to work with many of them. You

 can also use both HTTP and SOCKS proxies to transfer files to and from FTP

 servers.

 Get an ftp file using an HTTP proxy named my-proxy that uses port 888:

        curl -x my-proxy:888 ftp://ftp.leachsite.com/README

 curl also supports SOCKS4 and SOCKS5 proxies with --socks4 and --socks5.

 See also the environment variables Curl support that offer further proxy

 See also the environment variables Curl supports that offer further proxy

 control.

 Most FTP proxy servers are set up to appear as a normal FTP server from the

 client's perspective, with special commands to select the remote FTP server.

 curl supports the -u, -Q and --ftp-account options that can be used to

 set up transfers through many FTP proxies. For example, a file can be

 uploaded to a remote FTP server using a Blue Coat FTP proxy with the

 options:

   curl -u "Remote-FTP-Username@remote.ftp.server Proxy-Username:Remote-Pass" \

    --ftp-account Proxy-Password --upload-file local-file \

    ftp://my-ftp.proxy.server:21/remote/upload/path/

 See the manual for your FTP proxy to determine the form it expects to set up

 transfers, and curl's -v option to see exactly what curl is sending.

RANGES

  With HTTP 1.1 byte-ranges were introduced. Using this, a client can request