Responsive discussion avatars

Look at label of tin to see what it does.
Or see here:

![avatars](https://cloud.githubusercontent.com/assets/31692/3186485/173f6628-eca3-11e3-8ab4-a702cfab1cab.png)
![avatars-large](https://cloud.githubusercontent.com/assets/31692/3186484/173f3e3c-eca3-11e3-9432-6bbd23224bd8.png)

Credits to @alastairjardine for posing for screengrabs.