class.dropshadow.php: Create images/thumbnails with a drop-shadow effect

This class allows for easy creation of thumbnail images with (or without!) a drop shadow effect. Images can be read from a file or passed as a string (as you might take the images from a database), and they can also be resized for easy creation of thumbnails. You can also change the background colour of the image and generate the correct colour shadow. You can also use this class just to create the thumbnail images without a drop shadow effect. Images can be resizes in a variety of different ways, either as an absolute value or relative, to or by an amount, and as a pixel or percentage value.