fltk-egui

This is a proof of concept for an FLTK backend for Egui using a GlutWindow. The code is largely based on https://github.com/ArjunNair/eguisdl2gl and https://github.com/not-fl3/egui-miniquad (to a lesser extent); modified for fltk-rs.

To run the examples, just run: $ cargo run --example demo_lib $ cargo run --example triangle $ cargo run --example basic $ cargo run --example embedded

A demo app can be found here: https://github.com/fltk-rs/demos/tree/master/egui-demo

Todo

• Properly handle resizing the GlutWindow: ✅
• Support eguidemolib crate directly: ✅