improvments: removed use of images, added color and size properties

+0.3 Improvments:
 +- The plugin no longer uses images for sparks (should load faster and gives the freedom to change the color without modifying the image)
 +- properties minPixel and maxPixel used to specify the min and max size of the fireflies
 +- color property used to specify the color of the fireflies
 +
 +Example:
 +
 +$.firefly({
 +	color: '#fff',
 +	minPixel: 1,
 +	maxPixel: 3,
 +	total : 65,
 +	on: 'header'
 +});