New logo

As per #46 the site needed a better logo. Note there are actually two versions of the logo—a white one for when the nav bar is transparent and a dark one for when the nav bar is white. I used SVG for maximum retina awesome without the @2x hassles. This will mean it won't work in <IE8 so we will need to look at that if the client requires support for legacy browsers. 

Just for reference: 
http://caniuse.com/#feat=svg
http://css-tricks.com/svg-fallbacks/