Merge pull request #2 from pfulton/master

A bit more cleanup.
Merge pull request #3 from pfulton/master

Refactor grid pseudo-selectors to use "...-of-type"
Write additional documentation to include mention of the Bearded Grid Gem.
Write documentation to help users understand how to install the gem.
Write documentation to help users understand how to configure the grid's "container" max-width property.