Deprecate arraydata()

Actually we would need to raise a (more visible) RuntimeWarning, because the
behaviour of arraydata() has already changed, and DeprecationWarnings are
invisible by default... but we are goinrg to remove arraydata() or make it
raise an exception, so this is good enough for now.

See #93

pyaims/src/sip/volume.tpl

@@ -761,7 +761,7 @@ The header contains all meta-data.
 
 %End
 
-  SIP_PYOBJECT arraydata() /Factory/;
+  SIP_PYOBJECT arraydata() /Deprecated,Factory/;
 %Docstring
 .. note::