Add an enumerate example

examples/enumerate.rs

@@ -0,0 +1,16 @@
+extern crate cpal;
+
+use cpal::*;
+
+fn main() {
+    let endpoints = cpal::get_endpoints_list();
+    
+    println!("Endpoints: ");
+    for (endpoint_index, endpoint) in endpoints.enumerate() {
+        println!("{}. Endpoint \"{}\" Audio formats: ", endpoint_index + 1, endpoint.get_name());
+        let formats = endpoint.get_supported_formats_list().unwrap();
+        for (format_index, format) in formats.enumerate() {
+            println!("{}.{}. {:?}", endpoint_index+1, format_index+1, format);
+        }
+    }
+}