Add example convert program

Author: mstoeckl

examples/convert.rs

@@ -0,0 +1,28 @@
+//! An example of opening an image.
+extern crate image;
+extern crate image_extras;
+
+use std::env;
+use std::error::Error;
+use std::path::Path;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    image_extras::register();
+
+    let (from, into) = if env::args_os().count() == 3 {
+        (
+            env::args_os().nth(1).unwrap(),
+            env::args_os().nth(2).unwrap(),
+        )
+    } else {
+        println!("Please enter a from and into path.");
+        std::process::exit(1);
+    };
+
+    // Use the open function to load an image from a Path.
+    // ```open``` returns a dynamic image.
+    let im = image::open(Path::new(&from)).unwrap();
+    // Write the contents of this image using extension guessing.
+    im.save(Path::new(&into)).unwrap();
+    Ok(())
+}