Add basic tests via CSSLint

[ericf]

We should add at least some very basic tests to Pure. At a bare minimum we can use CSSLint and we might want to hook it up via the Grunt plugin.

[ericf]

I have something working on a local branch. The CSSLint Grunt plugin is useful but it isn't great, so for now I'm adding a separate task grunt test which will do the linting and errors (exit 2) if there's any lint warning (there's no way with the Grunt plugin to only log warns) :-/ This way running grunt doesn't lint, but grunt release will lint before it continues building and bundling the release.

The current master has several lint errors (I already fixed some of them) which I consider real problems which we should fix.

[ericf]

Merged #65 which closes this.