Event-driven dialog queue, story flag command, mod unit tests

Push-based event chains, runtime fixes (single end, goto lifecycle, if,
busy box, held delay, empty options, timed/animated/effect actions), the
'flag name value' DSL command, autoplay --dialogs=N, 19 mod unit tests.

tests/ActionBackgroundShowHideTests.cs

@@ -0,0 +1,36 @@
+namespace Cthangover.Mods.Dialog.Tests
+{
+    using System.Threading.Tasks;
+    using Cthangover.Core.Mods.Testing;
+    using Cthangover.Mods.Dialog.Action.Impls;
+
+    /// <summary>
+    /// <see cref="ActionBackgroundShowHide"/> without <c>wait</c>: the dialog goes on at
+    /// once and the fade still plays to the end.
+    /// </summary>
+    public class ActionBackgroundShowHideTests
+    {
+        [ModTest("background_fade/no_wait_fade_completes", TimeoutSeconds = 10)]
+        static async Task NoWaitFadeCompletes(ModTestContext ctx)
+        {
+            var stage = await DialogStage.Create();
+            try
+            {
+                var after = new ProbeAction();
+                var dlg = new DialogQueue();
+                dlg.BackgroundShowHide(BackgroundActionType.Hide, 0.1f);
+                dlg.Queue.Add(after);
+
+                stage.Box.SetDialogQueueAndRun(dlg, null, 0, null);
+                ModAssert.Equal(1, after.Runs, "dialog does not wait for the fade");
+                await DialogStage.Seconds(0.4);
+
+                ModAssert.True(stage.Host.Modulate.A < 0.01f, $"background faded out (alpha {stage.Host.Modulate.A})");
+            }
+            finally
+            {
+                stage.Free();
+            }
+        }
+    }
+}