Consistency changes.

* Use https for GitHub links
* Remove unneeded end tags
* Move target attribute at the end
Losslessly compress PNG files.
Convert the thumbnails to 8-bit.

gw1web_thumb.png | Bin 12394 -> 5724 bytes
gw2web_thumb.png | Bin 12514 -> 5748 bytes
gw3web_thumb.png | Bin 17703 -> 7841 bytes
Add a local jquery fallback.
Add a Grunt based solution for local development and deployment.

See README.md for more info.
Add html5shiv.js and respond.js for older browsers.
Clean up CSS.

* add missing vendor prefixed properties
* use hex colors when possible
* be more explicit with the background property
* use proper gradients for all browsers
* remove the unneeded img/header_bg.png
Move favicon.ico in root.
Switch to jquery fancybox for the screenshots.
Add image dimensions.