[Xmonad] The great xmonad-class merge!

[Don Stewart]

sjanssen:
> I've merged all the changes from the xmonad-class branch to the core.  There
> are a few changes users and developers ought to be aware of.
> 
> Layout state (such as the currently selected layout, nmasters, the
> master/slave ratio split, etc.) now persists across restarts.  Because the old
> layout-resetting behavior of mod-q is sometimes useful, we've added
> mod-shift-space to the keybindings to reset layout settings on the current
> workspace.
> 
> Some contributed modules haven't been ported yet:
>     HintedTile
>     Magnifier
>     Mosaic
>     SimpleStacking
>     Spiral
>     SwitchTrans
> 
> Feel free to pitch in with the porting effort.
> 
> Developers will notice that we've moved from the record of functions approach
> to a Layout class.  So far, this has been a big win, allowing us to write
> layouts and layout transformers in a more structured fashion.  Porting simple
> layouts to the new system is fairly easy, see the core layouts for examples.
> 
> Special thanks to David Roundy and Andrea Rossato for initiating this branch
> and doing the lion's share of porting to the new system.
> 

A layout class has been a long standing design plan, to help make it
even easier to write nice shiny layouts. It's great we've got this in
now.

-- Don