Add CW keying, function key messages and the documentation

The function keys send through cwdaemon or a WinKeyer, with N1MM's message
macros. Escape stops sending.

Settings are read with the reflection serializer rather than a generated one:
the generated one hands back null for every property the file leaves out
instead of the value the property is declared with, which crashed the program
the first time a new setting was added.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Nonemm.Keying/CwDaemonSender.cs

@@ -0,0 +1,49 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+
+namespace Nonemm.Keying;
+
+/// Sends CW through `cwdaemon`, which keys the radio from a serial or parallel
+/// port and is what Linux stations usually run. Its protocol is one UDP
+/// datagram per command; escape sequences start with a 0x1B byte.
+public sealed class CwDaemonSender : MessageSender
+{
+    private readonly UdpClient socket = new();
+    private readonly IPEndPoint daemon;
+
+    public CwDaemonSender(string host = "127.0.0.1", int port = 6789)
+    {
+        daemon = new IPEndPoint(IPAddress.Parse(host), port);
+        IsReady = true;
+    }
+
+    public bool IsReady { get; private set; }
+
+    public Task SendAsync(string text, CancellationToken cancellation = default) =>
+        WriteAsync(Encoding.ASCII.GetBytes(text.ToUpperInvariant()), cancellation);
+
+    public Task AbortAsync(CancellationToken cancellation = default) =>
+        WriteAsync([0x1B, (byte)'4'], cancellation);
+
+    public Task SetSpeedAsync(int wordsPerMinute, CancellationToken cancellation = default) =>
+        WriteAsync(Escape('2', wordsPerMinute.ToString()), cancellation);
+
+    public void Dispose() => socket.Dispose();
+
+    private static byte[] Escape(char command, string argument) =>
+        [0x1B, (byte)command, .. Encoding.ASCII.GetBytes(argument)];
+
+    private async Task WriteAsync(byte[] message, CancellationToken cancellation)
+    {
+        try
+        {
+            await socket.SendAsync(message, daemon, cancellation).ConfigureAwait(false);
+        }
+        catch (SocketException e)
+        {
+            IsReady = false;
+            throw new InvalidOperationException($"could not reach cwdaemon at {daemon}: {e.Message}", e);
+        }
+    }
+}