Update all the readme links. Remove composers and populator. Add shepherd.

Hello @nicks, 

Please review the following commits I made in branch 'nick-links'.

482191005c2e399197ac617059e5e63f2ca5695f (2014-08-25 13:16:45 -0400)
Update all the readme links. Remove composers and populator. Add shepherd.

R=@nicks