Improve Module::get_input/send_output

[dcwhite]

Need to access by port name; add option check and maybe a null check; provide casting via template somehow.

[dcwhite]

Should look like:

MatrixHandle x = getRequiredInput(PortNameObject1);
FieldHandle y = getOptionalInput(PortNameObject2);

That is, a function that does all the checking and casting in one go, automagically based on the PortObject (type to be determined), with everything inferred via function template type deduction.

[dcwhite]

getRequiredInput<T>(int portIndex) works. Next is adding index info to the PortNameObjects.

[dcwhite]

New fancy getRequiredInput/sendOutput methods are available as of 90a8e43. We'll see how people like them. I'll make a new issue for figuring out how to completely eliminate the duplication with the HasNInputPort templates and these new macros.