Support for start='xs', end='xs' on Col (not just row)

[iiAtlas]

New react-flexbox-grid user but really enjoying the lib so far!

Currently the below does not work:

<Col xs={3} start="xs">
    <span className="EventCard-price">$42</span>
</Col>

but manually adding the class achieves the desired result:

<Col xs={3} className="start-xs">
    <span className="EventCard-price">$42</span>
</Col>

The same is true for end-xs, is this by design?

[sudopseudocode]

I, too, would appreciate this feature. Love this library, thanks for the work!