[Chart] A bunch of features and fixes.

[Tim Docker]

Thanks for pointing out this problem:

Mon Oct 31 03:42:49 EST 2011 malcolm.wallace at me.com
   * Fix a missing pattern-match crash.

This patch (alone) doesn't actually compile. It needs some type 
constraints propagated across several functions. I suspect these changes 
are embedded in one of the other patches.

I've pushed an alternate fix, that returns a Nothing pick value (rather 
than a default of 0) and doesn't need the additional type constraints.

Also, on this change:

Tue Jan 11 23:51:52 EST 2011  malcolm.wallace at me.com
   * New function stackLayout1sVertically.
   Taking inspiration from renderLayout1sStacked, this alternative version
   is intended for situations where not only are the Layout1s stacked
   vertically, but the x-axes must be aligned value-wise, and the y-axes
   share the same type.  A single title at the top is taken from the first
   Layout1, and all legends are combined into a single box at the bottom.
   There is a single display of x-axis labels also.

Is it actually desirable that the y-axes share the same type? Or is that 
just a side effect of the implementation? I wonder if the same GUI 
output could be generated from a function with the (more versatile) 
signature of:

stackLayout1sVertically :: (Ord x,Ord y) => [AnyLayout1 x] -> Renderable ()

Regards,

Tim



Tim