Added a ``transform`` property that returns a transformation that can be frozen to the data values
Fixed docstring
Transformation to freeze is not necessarily affine... but matplotlib provides a frozen() method that does what we need!
Added tests for BBox.transform
Mark failing test as xfail for now
Fix matplotlib interactive backend error
Merge pull request #13 from astrofrog/transform-v3

Added a ``transform`` property that returns a transformation that can be frozen to the data values