Deprecate CArray?

[mdickinson]

Behaviour-wise, CArray is functionally identical to Array. The only difference is that there's an attribute coerce with value True for CArray and False for Array; that value has no effect on the behaviour of either class.

I suspect that CArray is little-used within real code. We could consider deprecating it and recommending that users use Array instead.

For some history about how things ended up this way, see #547.