Split Headerer back out

This is in anticipation of making it a fully independent program. Currently, the only links to the rest of SabreTools are a few usability libraries that are mostly unnecessary. The main logic now lives as a separate library in SabreTools.Skippers.

Headerer/Features/DisplayHelpDetailed.cs

@@ -0,0 +1,35 @@
+using SabreTools.Help;
+
+namespace Headerer.Features
+{
+    internal class DisplayHelpDetailed : BaseFeature
+    {
+        public const string Value = "Help (Detailed)";
+
+        public DisplayHelpDetailed()
+        {
+            Name = Value;
+            Flags.AddRange(["??", "hd", "help-detailed"]);
+            Description = "Show this detailed help";
+            _featureType = ParameterType.Flag;
+            LongDescription = "Display a detailed help text to the screen.";
+        }
+
+        public override bool ProcessArgs(string[] args, FeatureSet help)
+        {
+            // If we had something else after help
+            if (args.Length > 1)
+            {
+                help.OutputIndividualFeature(args[1], includeLongDescription: true);
+                return true;
+            }
+
+            // Otherwise, show generic help
+            else
+            {
+                help.OutputAllHelp();
+                return true;
+            }
+        }
+    }
+}