`grunticon` as a multitask.

This breaks existing configurations!

With this pull, the `grunticon` task is a multitask. This allows multiple sets of icons to be built, and if no options are required, allows short notation:

    grunt.initConfig({
        grunticon: {
            'example/source': 'example/output',
            'full-example: {
                src: 'example/source',
                dest: 'example/output'
                /* additional options */
            }
        }
    });