Added the capability to attach custom getter/setter functions to wrap the input/output values for parameters.  This also serves as a replacement for the check_params features, as parameter validation can be implemented as a setter (though it might be desirable to add a separate validator function as well?)
Apparently on some Numpy versions (1.7.1 at least) Numpy scalar arrays are not being recognized as number.Number instances.  Not sure if that's somehow intentional or a bug.