Add shearing transformations to standard library

[fryguybob]

(Imported from http://code.google.com/p/diagrams/issues/detail?id=40. Original issue from byor...@gmail.com on August 16, 2011, 08:24:59 PM UTC)

Diagrams.TwoD.Transform ought to include some functions to perform shears. I suppose something like

{{{
-- | @shearx d@ is the linear transformation which is the identity on
-- y coordinates and sends @(0,1)@ to @(d,1)@.
shearX :: (Transformable t, V t ~ R2) => Double -> t -> t
}}}

etc., should do nicely.

Unfortunately we run into linguistic trouble here with the noun/verb scheme for naming transformation combinators: "shear" is both noun and verb. I suppose we could get away with "shearing".