Added powered by Github Pages to footer

Saw someone else with a wintersmith blog had done this and thought it was a good
idea.
Added mailchimp subscribe for updates form

It is not styled perfect and I am not sure it works properly yet.  It does show
up approximately where I want it and how I want it though.  Pushing to live and
we'll see if I can sign up for updates and get added to the mailchimp list I
created for the blog.