Add Spritesmith options to Grunt task

I needed to add padding around my sprite elements. This update allows you to pass along 'spritesmithOptions' with your other options so you can change the padding, the layout algorithm, etc., thusly:


    spritesheet: {
        build: {
            sprites: {
                'images/sprite.png': ['images/sprite/*.png']
            },
            sheet: 'styles/sprite.css',
            templateUrl: 'styles/_sprite.mustache',
            spritesmithOptions: {
                padding: 5,
                algorithm: 'binary-tree'
            }
        }
    }