realtime-voice-conversion based on last year's work

This is based on the work I did in (July - October)ish 2019 to get real
time voice conversion working. I've removed it from the `voder` library
and made it into an isolable program. I'll work on extending the
capabilities.

src/audio_queue.rs

@@ -0,0 +1,78 @@
+use zmq;
+use zmq::{Error, Socket};
+use std::collections::VecDeque;
+use std::sync::{RwLock, PoisonError};
+
+pub struct AudioQueue {
+  queue: RwLock<VecDeque<f32>>,
+}
+
+impl AudioQueue {
+  pub fn new() -> Self {
+    Self {
+      queue: RwLock::new(VecDeque::new()),
+    }
+  }
+
+  pub fn push_back(&self, val: f32) {
+    match self.queue.write() {
+      Ok(mut queue) => {
+        queue.push_back(val);
+      },
+      Err(_) => {
+        unreachable!("This shouldn't happen (push_back)");
+      },
+    }
+  }
+
+  pub fn extend(&self, buf: Vec<f32>) {
+    match self.queue.write() {
+      Ok(mut queue) => {
+        queue.extend(buf);
+      },
+      Err(_) => {
+        unreachable!("This shouldn't happen (extend)");
+      },
+    }
+  }
+
+  pub fn drain(&self) -> Vec<f32> {
+    match self.queue.write() {
+      Ok(mut queue) => {
+        return queue.drain(..)
+            .collect::<Vec<_>>();
+      },
+      Err(_) => {
+        unreachable!("This shouldn't happen (drain)");
+      },
+    }
+  }
+
+  pub fn drain_size(&self, size: usize) -> Option<Vec<f32>> {
+    match self.queue.write() {
+      Ok(mut queue) => {
+        if queue.len() < size {
+          return None;
+        }
+        let vec = queue.drain(0..size)
+            .collect::<Vec<_>>();
+
+        return Some(vec);
+      },
+      Err(_) => {
+        unreachable!("This shouldn't happen (drain_size)");
+      },
+    }
+  }
+
+  pub fn len(&self) -> usize {
+    match self.queue.read() {
+      Ok(mut queue) => {
+        return queue.len();
+      },
+      Err(_) => {
+        unreachable!("This shouldn't happen (len)");
+      },
+    }
+  }
+}