clipTo function

[fryguybob]

(Imported from http://code.google.com/p/diagrams/issues/detail?id=76. Original issue from byor...@gmail.com on March 15, 2012, 12:17:22 AM UTC)

Diagrams.TwoD.Path defines a function

clipBy :: (HasStyle a, V a ~ R2) => Path R2 -> a -> a

which applies a clipping path attribute to a diagram, but does not alter its envelope. We should also define a function 'clipTo' which does 'clipBy' and also clips the diagram's envelope. This should be possible, but is not entirely straightforward since it requires taking a pointwise minimum of the two envelopes, whereas the monoid instance for Envelope uses a pointwise maximum. But it should not be too hard to take a look at how the actual Monoid instance for Envelope is implemented, and imitate it.

[bergey]

This is satisfied by #144, right? @jeffreyrosenbluth @byorgey

[byorgey]

Yep!