Simplification of `compareWidths`.
Merge pull request #181 from ezequiel/comparewidth-fix

Simplification of `compareWidths`.
Add support for old IE versions of local CSS files

This allows the following:

    {{addLocalCSS "/css/home.css" hasOldIE=true}}

Which will wrap the `<link>` to "/css/home.css" in an IE conditional
comment and serve up "/css/home-old-ie.css" to IE < 9.
Remove test hasOldIE from Blog layout
Fix combo of local CSS to only use IE conditional comments when needed
Fix layout downloads' `pure` context
committed by screwdriver build
initial pass at changing main.css to be mobile-first
Initial commit of Gruntfile.js and grid_units grunt task

This Gruntfile generates the responsive grid needed for the Pure Site
via rework-pure-grids.

As of this commit, we need to fix
https://github.com/ericf/rework-pure-grids/issues/6 so until we do that,
you have to manually remove the non-media query rules from the outputted
CSS.
remove pure-g-r and add responsive-grid.css to layout
update home.handlebars to use mobile-first grid
update partials/base/* to use mobile-first grid
update forms/multi.handlebars to use mobile-first grid
update legal.handlebars to use mobile-first grid
remove .pure-g-r rule from main.css
Update Gruntfile.js

Updated the grid that we generate based on the needs of grid doc.
Update grid docs with mobile-first grid info

This commit updates the Grids documentation with the following:

* How to generate a mobile-first grid
* How to use rework-pure-grids
* Examples
* Removal of partials/examples that don't apply anymore
Merge pull request #182 from ericf/old-ie-css

Add support for old IE versions of local CSS files
Merge branch 'master' into mobile-first
Revert "Update grid docs with mobile-first grid info"

This reverts commit 990b51d0009229d4547af2029f3cba508788c777.