[cairo] Adding cairo_shear and family

[Behdad Esfahbod]

James Cloos wrote:
>>>>>> "Behdad" == Behdad Esfahbod <behdad at behdad.org> writes:
> 
> Behdad> s/sheer/shear/ I guess?
> 
> Yes, with that.  I used sheer in the sense of its nautical meaning, but
> dict(1) confirms that the affine transformation is in fact shear....
> 
> [SIGH]
> 
> A corrected patch is below.
> 
> Behdad> The docs can be more specific.
> 
> I added a note to each /** */ block noting the shear matrix.
> 
> -JimC

Thanks Jim.

+ * Shearing multiplies the current transformation by the matrix:
+ *
+ * 1  sx 0
+ * sy 1  0
+ * 0  0  1

Does this come out correctly in the generated docs?  Guess not.  Also, cairo
matrices are 3x2 not 3x3.  And we don't refer to them in the matrix form
anyway.  Maybe replace that with [1 sx sy 1 0 0].

Other than that, looks good to go in.  Oh, the docs lack the Since: tag.

behdad