Updated the what's new. Better, but not complete.

How's about ...

```This means that when performing cube arithmetic the dimensionality and shape of cubes do not need to match. For example, if the dimensionality of a cube is reduced by collapsing, then the result can be used to subtract from the original to calculate an anomoly::

    >>> time_mean = original_cube.collapsed('time', iris.analysis.MEAN)
    >>> mean_anomoly = original_cube - time_mean

Given both broadcasting **and** coordinate meta-data, Iris can now perform arithmetic with cubes which do not have the same shape::

    >>> other = original_cube.copy()
    >>> other.transpose()
    >>> zero_cube = orginal_cube - other
```