Version bump on lens

Builds fine under lens HEAD
Merge pull request #123 from nandykins/master

Version bump on lens
Updated Arrowhead.hs with diagrams-haddock
Added example diagrams to haddock
added annularWedge to TwoD.Arc
renamed r2
moved origin to center of circle
Merge pull request #124 from diagrams/lens

Convert from newtype to lens
use lens for TransInv type