impl Debug for Device (#253)

The internal alsa, null and emscripten Device implementations already
implemented Debug; but the coreaudio and wasapi ones, and therefore
also the wrapper, did not.

I decided to eschew the `Device(…)` wrapping in the outer layer
(hence a custom implementation rather than `#[derive(Debug)]`),
because `Device(Device)`, `Device(Device { … })` and so forth all
look better without the extra `Device(…)` wrapping.

On the wasapi and coreaudio implementations I put both the pointer and
name. Name because it’s useful, pointer because on Windows at least
I believe duplicated names are possible. (e.g. two monitors that include
monitors, of the same type; I haven’t strictly confirmed this, because I
killed those off harshly on my machine and don’t want to reinstate
them.)

I do not have access to a macOS device to confirm that the coreaudio
implementation is sane, but I think it is.

src/coreaudio/mod.rs

@@ -15,6 +15,7 @@ use UnknownTypeInputBuffer;
 use UnknownTypeOutputBuffer;
 
 use std::ffi::CStr;
+use std::fmt;
 use std::mem;
 use std::os::raw::c_char;
 use std::ptr::null;
@@ -302,6 +303,15 @@ impl Device {
     }
 }
 
+impl fmt::Debug for Device {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Device")
+            .field("audio_device_id", &self.audio_device_id)
+            .field("name", &self.name())
+            .finish()
+    }
+}
+
 // The ID of a stream is its index within the `streams` array of the events loop.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct StreamId(usize);

src/lib.rs

@@ -395,6 +395,12 @@ impl Device {
     }
 }
 
+impl fmt::Debug for Device {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, f)
+    }
+}
+
 impl EventLoop {
     /// Initializes a new events loop.
     #[inline]

src/wasapi/device.rs

@@ -1,5 +1,6 @@
 use std;
 use std::ffi::OsString;
+use std::fmt;
 use std::io::Error as IoError;
 use std::mem;
 use std::ops::{Deref, DerefMut};
@@ -552,6 +553,15 @@ impl Clone for Device {
     }
 }
 
+impl fmt::Debug for Device {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Device")
+            .field("device", &self.device)
+            .field("name", &self.name())
+            .finish()
+    }
+}
+
 impl Drop for Device {
     #[inline]
     fn drop(&mut self) {