executable: add scene parsing and rendering

src/main.rs

@@ -1,3 +1,24 @@
-fn main() {
-    println!("Hello, world!");
+use pathtracer::render::Scene;
+use std::path::PathBuf;
+use structopt::StructOpt;
+
+#[derive(StructOpt, Debug)]
+struct Options {
+    /// Input description for the scene to be rendered.
+    #[structopt(short, long, parse(from_os_str), default_value = "scene.yaml")]
+    input: PathBuf,
+    /// Output image for the rendered scene.
+    #[structopt(short, long, parse(from_os_str), default_value = "scene.png")]
+    output: PathBuf,
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let options = Options::from_args();
+    let f = std::fs::File::open(options.input)?;
+
+    let scene: Scene = serde_yaml::from_reader(f)?;
+    let image = scene.render();
+
+    image.save(options.output)?;
+    Ok(())
 }