Improve profiling API, add documentation

[Andrew Lunn]

profile.c:

    // Create a TFTP server to provide the data
    tftp_server_id = tftpd_start(0, &profile_fileops);
}

Please could you make the port number CDL configurable. I have
applications that use the TFTP server as well. In this situation i
would want the profile TFTP server on another port. 

      Thanks
            Andrew