Allow span mixins to define float direction

[pixelwhip]

One of the nice features of zen-grids and the isolation method is being able to control the float direction when spanning the grid. This is super helpful when you 3 divs and a two column layout. You may want the 1st to float left; 2nd to float right and clear none; the 3rd to float left and clear left. This allows the 3rd div to sit below the 1st regardless of the length of the 2nd.

I've messed with the $direction variable. It does the trick in terms of the CSS output I'm looking for except it also adds the [dir="rtl"] selector. A nice feature, but in this case I'm not trying to change the language direction, just the float direction for layout purposes.

I noticed the rtl selector used to be configurable and I thought I could set it to ''; but that seems super hacky anyway.

I also tried setting the direction on the span mixin itself but it only affects clearing, not floats and margins.

Is there a way to do this that I'm missing?

[scottkellum]

@pixelwhip I think we may need to add something for this use case.

[Snugug]

With improvements made in #157, we should be able to implement this fairly easily.

[pixelwhip]

Yeeeeeeeeahhhhhhhhh!!!!! Thanks. I'll be trying this out real soon.

[Snugug]

I realized my logic for this is probably off, so I should look into this again.