Added device images:

- iPhone 6 (img/iPhone.svg)
  original image from http://www.graphberry.com/item/free-iphone-6mockups/
- iPad (img/iPad.svg)
  original image from http://dtailstudio.com/mobile-devices

Exported using SVG 1.1 with fonts converted to outlines.
Compatibility chart: http://caniuse.com/#feat=svg