/**
 * 获取Gravatar头像
 * 
 * http://en.gravatar.com/site/implement/images/
 * @param $email
 * @param $s size
 * @param $d default avatar
 * @param $g
 * @author 编程之家 jb51.cc jb51.cc
 */
function getGravatar($email,$s = 40,$d = 'mm',$g = 'g') {
 $hash = md5($email);
 $avatar = "http://www.gravatar.com/avatar/$hash?s=$s&d=$d&r=$g";
 return $avatar;
}