Do a better job resizing images

[byorgey]

Instead of calling C.setSourceSurface (https://github.com/diagrams/diagrams-cairo/blob/master/src/Diagrams/Backend/Cairo/Internal.hs#L292) we ought to use withPatternForSurface to create a Pattern first, then apply patternSetFilter to set the Filter (http://hackage.haskell.org/packages/archive/cairo/0.12.4/doc/html/Graphics-Rendering-Cairo.html#t:Filter) to something other than the default. (Is there a best choice or should we make it configurable somehow? Perhaps an attribute?) Then finally we can call setSource with the pattern.