Vendor dependencies for 0.3.0 release

vendor/gltf/examples/roundtrip/main.rs

@@ -0,0 +1,21 @@
+use std::{fs, io};
+
+use std::boxed::Box;
+use std::error::Error as StdError;
+
+fn run(path: &str) -> Result<(), Box<dyn StdError>> {
+    let file = fs::File::open(path)?;
+    let reader = io::BufReader::new(file);
+    let gltf = gltf::Gltf::from_reader(reader)?;
+    let json = gltf.document.into_json().to_string_pretty()?;
+    println!("{}", json);
+    Ok(())
+}
+
+fn main() {
+    if let Some(path) = std::env::args().nth(1) {
+        run(&path).expect("runtime error");
+    } else {
+        println!("usage: gltf-roundtrip <FILE>");
+    }
+}