Added tests to verify that {{ 'now' | date :'%Y' }} and {{ 'today' | date :'%Y' }} work.

In the case of Ruby 1.9.3, 'now' is no longer parsed.  For safe
measures, I've added 'today' as well.
Merge branch 'master' of git://github.com/Shopify/liquid

* 'master' of git://github.com/Shopify/liquid:
  * Seperated 'Howto' into 'How to'. * Added periods to the second list as the first item has them. I guess I'm anally retentive like that. :)
  Fix conditions using negative number comparisons
Merge branch 'master' of https://github.com/ndwebgroup/liquid into ndwebgroup-master