draft implementation of include statement and FunctionCall ScadObject

[RustyJoeM]

I tried to quickly look into docs, but the amount felt a bit scary... :) thus no committed usage example.
Adding code snippet here, to get a feel on how to use this:

    // add include statement to the top of resulting OpenSCAD file:
    let mut scad_file = ScadFile::new();
    scad_file.add_include("SomeCustom.scad".to_string());

    // and someplace where building ScadObjects:
    let fn_name = "SomeScadFunction".to_string();

    // can add items of different types into arguments vector
    let fn_args: FnCallArgs = vec![Box::new(vec2(3.0, 4.0)), Box::new(1.0)];

    // can add items of different types into named arguments vector as well
    let fn_named_args: FnCallNamedArgs = vec![
        ("resolution".to_string(), Box::new(123)),
        ("centered".to_string(), Box::new(false)),
    ];

    let scad_object = scad!(FunctionCall(
        fn_name,
        Some(Rc::new(fn_args)),
        Some(Rc::new(fn_named_args))
    ));

    scad_file.add_object(scad_object);

results in following code neing generated:

    include <SomeCustom.scad>
    SomeScadFunction([3,4], 1, resolution = 123, centered = false);

[TheZoq2]

Sorry for the delay!

Overall, it looks like a nice change, though I'm not sure about all the Box and Rc stuff, do you think there is a way to get rid of it?

Edit: So github will auto close the corresponding issue. Closes #7

[RustyJoeM]

As i'm not yet professionally experienced in Rust, "architecture"/design review would be definitely welcome :)

It is needed to allow different types of items to be in the same vector in my current understanding, but...
Maybe it would be better to simplify my proposed API, and remove boxing/rc-ing by hiding from user, - e.g. define add_(named_)parameter() function for params struct and build it step-by-step invoking add_param() with simple references/owned values.

I'll try to make alternative implementation for this and see if it's cleaner/simpler. Will keep you updated...

[TheZoq2]

Yea, I figured that was the case. Like you said, the builder pattern might look nicer here, something like

function
    .param(x)
    .named_param(name, y)
    .build()