feat: video publishing (#42)

- Prepare webrtc abstraction ( for future wasm support )
- Added track publish support for videos
  - Added LogoTrack example to simple_room demo
- Lot of cleanup
- There are compiler warnings I'll solve on our v1 release

livekit-webrtc/src/video_stream.rs

@@ -0,0 +1,54 @@
+use crate::imp::video_stream as stream_imp;
+
+// There is no shared sink between native and web platforms.
+// Each platform requires different configuration (e.g: WebGlContext, ..)
+
+#[cfg(not(target_arch = "wasm32"))]
+pub mod native {
+    use super::stream_imp;
+    use crate::media_stream::RtcVideoTrack;
+    use crate::video_frame::BoxVideoFrame;
+    use futures::stream::Stream;
+    use std::fmt::Debug;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    pub struct NativeVideoStream {
+        pub(crate) handle: stream_imp::NativeVideoStream,
+    }
+
+    impl Debug for NativeVideoStream {
+        fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+            f.debug_struct("NativeVideoStream")
+                .field("track", &self.track())
+                .finish()
+        }
+    }
+
+    impl NativeVideoStream {
+        pub fn new(video_track: RtcVideoTrack) -> Self {
+            Self {
+                handle: stream_imp::NativeVideoStream::new(video_track),
+            }
+        }
+
+        pub fn track(&self) -> RtcVideoTrack {
+            self.handle.track()
+        }
+
+        pub fn close(&mut self) {
+            self.handle.close();
+        }
+    }
+
+    impl Stream for NativeVideoStream {
+        type Item = BoxVideoFrame;
+
+        fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
+            Pin::new(&mut self.get_mut().handle).poll_next(cx)
+        }
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+pub mod web {}