Support for milligram's flexbox-based columns

milligram's flexbox-based column selectors and rules have their own section in sscaffold and are largely unchanged, with one important exception: milligram's .container selector has been replaced by the main article, main section, main section > *, and main article > * selectors later in the file, in the "theme" section.

Rows and columns need to be inside any block-level element inside a section or article element inside the main element to prevent conflicts between milligram's .row rules and other selectors:

<body>
    <main>
        <section>
            <div>
                <div class="row">
                    <div class="column">
                        <!-- ... -->
                    </div>
                </div>
            </div>
        </section>
    </main>
</body>

You can see a more complete example on sscaffold-css.com, which is also a handcrafted, not-minified demo page.

There is a more complete explanation of this change on the differences from milligram page.