Pure-rust implementation of NanoVG

Demos

Simple square `cargo run -p nvg-gl --example demo-square` The tiniest way to use nvg+glutin, can help beginner to start with nvg.
Clock `cargo run -p nvg-gl --example demo-clock`
Cutout `cargo run -p nvg-gl --example demo-cutout`
Draw `cargo run -p nvg-gl --example demo-draw`