pass a few more arguments down to sass

I've added `unixNewlines`, `precision`, and `cacheLocation`

`precision` is especially important for folks who use twitter
bootstrap as precision needs to be set to 10, but the default
is 5.
update for broccoli 0.13
Merge branch 'more-sass-cli-options' of github.com:jrobeson/broccoli-ruby-sass into jrobeson-more-sass-cli-options
remove cacheLocation, add more docs from PR