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.Session/MessageExpander.cs

@@ -0,0 +1,63 @@
+using System.Text;
+
+namespace Nonemm.Session;
+
+/// Fills in a function key message. The macro names are N1MM's, so a message
+/// file written for either program says the same thing.
+public static class MessageExpander
+{
+    /// Cut numbers: a contest operator sends T for zero and N for nine because
+    /// they are shorter.
+    private const string CutDigits = "T12345678N";
+
+    public static string Expand(string template, LoggingSession session)
+    {
+        StringBuilder text = new();
+        int at = 0;
+        while (at < template.Length)
+        {
+            char c = template[at];
+            if (c == '{')
+            {
+                int close = template.IndexOf('}', at + 1);
+                if (close < 0)
+                {
+                    text.Append(template[at..]);
+                    break;
+                }
+                text.Append(Macro(template[(at + 1)..close], session));
+                at = close + 1;
+                continue;
+            }
+            if (c == '#')
+            {
+                text.Append(session.SentNumber);
+                at++;
+                continue;
+            }
+            text.Append(c);
+            at++;
+        }
+        return text.ToString();
+    }
+
+    private static string Macro(string name, LoggingSession session) => name.ToUpperInvariant() switch
+    {
+        "MYCALL" => session.Me.Callsign,
+        "CALL" => session.Entry.Call.Trim(),
+        "LOGGEDCALL" => session.Log.Qsos.Count > 0 ? session.Log.Qsos[^1].Call.Text : "",
+        "EXCH" => session.Instance.SentExchange,
+        "SENTRST" => session.DefaultReport(),
+        "SENTRSTCUT" => Cut(session.DefaultReport()),
+        "SENTNR" => session.SentNumber.ToString(),
+        "SENTNRCUT" => Cut(session.SentNumber.ToString()),
+        "NAME" => session.Me.Name,
+        "GRIDSQUARE" => session.Me.GridSquare,
+        "MYZONE" => session.Me.CqZone.ToString(),
+        "OTHERMHZ" => (session.Frequency.Megahertz).ToString("0.###"),
+        _ => "",
+    };
+
+    private static string Cut(string digits) =>
+        new(digits.Select(d => char.IsAsciiDigit(d) ? CutDigits[d - '0'] : d).ToArray());
+}