Remove vows

Hey @NickQiZhu, @jrideout, @gordonwoodhull,

This gets rid of vows, sinon, and jsdom.

This also introduces a regression test using phantomjs similar to the web-test written in vows. This required some complicated diffing, because phantomjs on different platforms seems to render svg node attributes with slightly different (usually < 0.003) precision. I'm still working on getting this passing on CI.

The row chart specs only run one set of data (instead of positive, negative, and mixed data). Therefore, I'm opening this as a pull request for review before merging it in (@leotcsun, was there a reason we were doing this?).

Thanks!
Stephen & David