UIImage调整大小：通过这个链接。

UIImage resize : Go thru this link.

感谢Paul Lynch。

Thanks to Paul Lynch.

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}