switch to a modified version of Bourbon instead of Compass

The most recent version of Bourbon (4.0.0-rc1) is not compatible with
whatever the current version of libSass (used by gulp-sass). I removed
the problem files, and it seems to work fine.
replaced modified Bourbon with node-bourbon because that was a bad idea.

Not sure what version of Bourbon node-bourbon is using, but it hasn’t
been updated in 7 months. Is at least up to date with 3.0, although 3.2
didn’t work when I tried that version out.
Merge branch 'with-bourbon'