Created SASS input directory

Gonna use SASS to build Chassis from here on out. First step: set up
file structure.
Streamlining

Clearing out some code that just wasn’t needed.
Cleared out some cruft
Stopped tracking the sass-cache folder
Added some extra info
Simplified math

Updated the instructions to reflect the simpler SASS structure.
Abstracted variables

Grid measurements are now contained in _variables.scss, so you can
update the entire grid by tweaking one file.
updated
Merge branch 'dev'