Optional widescreen / high resolution media query and mixin.

Provisional pull request, as i'm curious about your opinion for this...

I've added an optional widescreen / high resolution media query and mixin to accomodate for scenarios where a layout for larger screens is desired.

I'm currently using inuit on a fairly ambitious project at the moment, and so far, i'm finding it very hard to fault :) I actually started off writing my own OOCSS framework, but it escalated out of control fairly quickly as i needed more and more design patterns. 

Anyway, i've found that i want to accomodate for hi resolution screens on this project. Normally percentages would work fine for hi-resolution layouts, but the complexity of this project demands an extra breakpoint for hi resolution screens.

Take a look at the pull request and let me know what you think. It's all optional and will be turned off by default, and i've tried to comment and name the variables as best i can.