Add debugging support to asset minification

We’ve added an option to the css_minify_tag liquid filter. For instance, if you had a config.yml file with the following:

css:
  all:
    - blue.css
    - css/red.css
    - /test.css

When you added this to your theme.liquid (note the new true option after css_minify_tag):

{{ "all" | css_minify_tag: true }}

It would render as:

<link href="/files/assets/blue.css?1340564403" type="text/css" media="screen" rel="stylesheet" />
<link href="/files/assets/css/red.css?1340564403" type="text/css" media="screen" rel="stylesheet" />
<link href="/test.css?1340564403" type="text/css" media="screen" rel="stylesheet" />