align and friends should be in terms of a new 'Alignable' class instead of 'Boundable'

[fryguybob]

(Imported from http://code.google.com/p/diagrams/issues/detail?id=64. Original issue from byor...@gmail.com on January 22, 2012, 06:22:36 PM UTC)

The fact that 'align' and friends currently require a Boundable constraint is an implementation detail. Things that are Boundable can certainly be aligned using the current code. However, there are other things which are not Boundable but which it makes sense to align: the particular motivating example being animations.

Just as was already done with the new Juxtaposable class, aligning ought to be done in terms of a new class, something like

class Alignable a where
alignBy :: V a -> Scalar (V a) -> a -> a

with a function 'alignByDefault' provided which gives the current implementation in terms of Boundable etc. Then we can also make an Alignable instance for animations, which simply does the alignment pointwise over time.