Add more detailed message to panic

When samples format is not supported, cpal panics with "not yet implemented" message, which is not useful in bug reports.
This adds samples format to the message.

Signed-off-by: Mariusz Ceier <mceier+cpal@gmail.com>

src/wasapi/mod.rs

@@ -41,7 +41,7 @@ impl Voice {
     pub fn get_samples_format(&self) -> ::SampleFormat {
         match self.bits_per_sample {
             16 => ::SampleFormat::I16,
-            _ => unimplemented!(),
+            _ => panic!("{}-bit format not yet supported", self.bits_per_sample),
         }
     }