fltk-flow

A crate wrapping Fl_Flow. This uses a native module written in C++, so it won't work with the fltk-bundled feature.

Example:

```rust

![allow(unused_mut)]

use fltk::{prelude::, enums::, *}; use fltk_flow::Flow;

fn main() { let a = app::App::default().with_scheme(app::Scheme::Gtk);

let mut win = window::Window::default().with_size(640, 480);
let mut flow = Flow::default_fill();
let btn = button::Button::default().with_size(100, 30).with_label("Button1");
let inp = input::Input::default().with_size(150, 30);
let mut sep = frame::Frame::default().with_size(10, 1);
let area = input::MultilineInput::default().with_size(10, 10);
let mut sep2 = frame::Frame::default().with_size(10, 1);
let btn2 = button::Button::default().with_size(100, 30).with_label("Button2");
flow.end();
win.end();
win.resizable(&flow);
win.show();

sep.set_color(Color::Black);
sep.set_frame(FrameType::FlatBox);
sep2.set_color(Color::Black);
sep2.set_frame(FrameType::FlatBox);

flow.rule(&btn, "^<");
flow.rule(&inp, "^<");
flow.rule(&sep, "=<^");
flow.rule(&area, "<^");
flow.rule(&sep2, "=<^");
flow.rule(&btn2, "v");
flow.rule(&sep2, "v");
flow.rule(&area, "=>=v");

a.run().unwrap();

} ```