Need require in the sprockets plugin's stylesheet modules as well.

Needed on ruby 2.0.0 on x86 but not x86_64 (for me at least).
Expose production_url

For some reason, `{{ urls.production_url }}` no longer works. This might
not be the correct fix but it works.
Make dates formattable

This commit makes the date format customizable via the `date_format`
option. While this option is site-wide, specific dates can be formated
with `{{#date.strftime}}format_string{{/date.strftime}}`.

closes ruhoh/ruhoh.rb#69
Fix logging error.
Add test cases for date formatting.