Support animations

[hrj]

• [X] Prelim support for animations
• [ ] Playback speed. flif encoder now has the -F option to specify frame delay.
• [ ] loop control
• [ ] immediate playback (play as soon as some frames are available).

[hrj]

Image References: http://littlesvr.ca/apng/gif_apng_webp2.html

http://www.buzzhunt.co.uk/2009/06/12/simple-mechanisms-explained/

http://bellard.org/bpg/animation.html

http://blog.gaborit-d.com/40-cinemagraph-inspiration/