Add IE11 as a supported browser

I checked browser compatibility for Bootflat in Windows 8.1 and with IE 11 using BrowserStack and the site rendered fine. See here for screenshot: http://awesomescreenshot.com/0562j4ni1f

Afterwards, I edited the pages which referred to browser compatibility and added IE 11.

Cheers
![screen shot 2014-03-22 at 5 56 47 pm](https://f.cloud.github.com/assets/3394807/2490173/17d4d6a4-b198-11e3-9b35-6c47b0aec437.png)