title: How to offset flex item?
body: <p>I'm developing a pure flexbox grid framework called <a href="https://github.com/ryanve/flexboxes" rel="noreferrer">flexboxes</a>. I'm looking to implement a way to offset flex items by a particular number of grid columns in any <code>flex-direction</code>. <a href="https://codepen.io/ryanve/pen/jmjMoJ" rel="noreferrer">This is possible with percentage margin but can it be done in a simpler way using flex properties?</a> With what's available in <a href="https://github.com/ryanve/flexboxes/tree/v0.4.0" rel="noreferrer">flexboxes@0.4.0</a>?  I'd rather not implement margin classes this way because doing to would seemingly require adding classes for all 4 directions to accommodate all <code>flex-direction</code> values.</p>