Bower compatibility for node based projects

My team is utilizing this version of Susy, it actually works great, but we are moving to a node based workflow and would like to be able to pull in this version via bower.
Correct the version to 2.0.0-alpha.4

According to [semver #9](http://semver.org), the prerelease version uses a hyphen.
Merge pull request #239 from stephenway/patch-1

Bower compatibility for node based projects
Unify syntax parsing, fixes #249
Padding mixins respect inside gutters
Bump version to 2.0.0.alpha.6.
Update Bower version
Update changelog
Rake record-version commits bower changes
Update test gems
Add validation for columns, gutters, and column-width
Fix warning output from math validation
Degbug grids are hidden by default
Remove nth-first/-last mixins as out-of-scope
Allow gutter syntax to take context-only without "of"
Add global box sizing controls
Fixed SASS_PATH environment variable

Make it compatible with sass and sass-rails gems.

After changing the environment variables from SASSPATH
to SASS_PATH, Susy 2 worked flawlessly on Rails 4 and
Sinatra applications, without the compass dependency.
Fix typo
Remove box-sizing from global settings
Gallery and span account for global-box-sizing