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/WinkeyerSender.cs

@@ -0,0 +1,72 @@
+using System.IO.Ports;
+using System.Text;
+
+namespace Nonemm.Keying;
+
+/// Sends CW through a WinKeyer on a serial port. The keyer is opened in host
+/// mode, which is the state where it takes text rather than following a paddle
+/// alone.
+public sealed class WinkeyerSender : MessageSender
+{
+    private const byte AdminCommand = 0x00;
+    private const byte HostOpen = 0x02;
+    private const byte HostClose = 0x03;
+    private const byte SetSpeed = 0x02;
+    private const byte ClearBuffer = 0x0A;
+
+    private readonly SerialPort port;
+
+    public WinkeyerSender(string portName, int baudRate = 1200)
+    {
+        port = new SerialPort(portName, baudRate, Parity.None, 8, StopBits.Two);
+    }
+
+    public bool IsReady => port.IsOpen;
+
+    /// Opens the port and puts the keyer in host mode. The keyer answers with
+    /// its firmware version, which is read and thrown away.
+    public void Open()
+    {
+        port.Open();
+        port.Write([AdminCommand, HostOpen], 0, 2);
+        Thread.Sleep(100);
+        port.DiscardInBuffer();
+    }
+
+    public Task SendAsync(string text, CancellationToken cancellation = default)
+    {
+        Write(Encoding.ASCII.GetBytes(text.ToUpperInvariant()));
+        return Task.CompletedTask;
+    }
+
+    public Task AbortAsync(CancellationToken cancellation = default)
+    {
+        Write([ClearBuffer]);
+        return Task.CompletedTask;
+    }
+
+    public Task SetSpeedAsync(int wordsPerMinute, CancellationToken cancellation = default)
+    {
+        Write([SetSpeed, (byte)Math.Clamp(wordsPerMinute, 5, 99)]);
+        return Task.CompletedTask;
+    }
+
+    public void Dispose()
+    {
+        if (port.IsOpen)
+        {
+            port.Write([AdminCommand, HostClose], 0, 2);
+            port.Close();
+        }
+        port.Dispose();
+    }
+
+    private void Write(byte[] message)
+    {
+        if (!port.IsOpen)
+        {
+            throw new InvalidOperationException($"the keyer on {port.PortName} is not open");
+        }
+        port.Write(message, 0, message.Length);
+    }
+}