smarty: add support for angled quotes

Such quotes are used in French, Russian/Ukrainian/Belorussian, German and many other languages. See <http://en.wikipedia.org/wiki/Guillemet> for details.

Now smartypants will convert `<<` to `«` and `>>` to `»` if the corresponding option is set (disabled by default).
Shouldn't that be `smart_angled_quotes` (you're missing the 'd')? I believe that is why the Travis build failed. Fix it and I'll merge. I think this is agreat addition.