examples: add a simplified bytebeat player to show how to use sokol.audio, and that does not depend on gg

examples/sokol/sounds/simple_bytebeat.v

@@ -0,0 +1,35 @@
+// This program illustrates how to use sokol.audio in a simple console app, *without a gui*.
+// See melody.v for an example of how it can be integrated into a graphics app.
+import time
+import sokol.audio
+
+fn audio_callback(mut soundbuffer &f32, num_frames int, num_channels int, mut frame_0 &i32) {
+	for frame := 0; frame < num_frames; frame++ {
+		t := i32(f32(*frame_0 + frame) * 0.245)
+		y := (t * (((t / 10 | 0) ^ ((t / 10 | 0) - 1280)) % 11) / 2 & 127) +
+			(t * (((t / 640 | 0) ^ ((t / 640 | 0) - 2)) % 13) / 2 & 127)
+		for ch := 0; ch < num_channels; ch++ {
+			idx := frame * num_channels + ch
+			a := f32(y - 127) / 255.0
+			soundbuffer[idx] = a
+		}
+	}
+	frame_0 += num_frames
+}
+
+// The example uses \r, to show a simple progress bar, while the music is playing.
+// That works best, if the output is not buffered at all.
+unbuffer_stdout()
+
+println('The ByteBeat formula used in this example is from https://www.youtube.com/watch?v=V4GfkFbDojc , "Techno" by Gabriel Miceli')
+
+mut frame_0 := i32(0) // offset of the current audio frames, relative to the start of the music
+audio.setup(stream_userdata_cb: audio_callback, user_data: &frame_0) // our state/user_data can be just a simple integer
+
+for t in 0 .. 600 {
+	print('\r> t: ${t:5}s , frame_0: ${frame_0:10} samples')
+	time.sleep(1 * time.second)
+}
+println('\nGood bye.')
+
+audio.shutdown()