Show Pending in either Today's list of the Future list, but not both at the same time.

src/pit.nim

@@ -263,7 +263,11 @@ proc list(
   if future:
     if today: ctx.writeHeader("Future")
 
-    for s in [Pending, Todo]:
+    let futureCategories =
+      if showToday: @[Todo]
+      else: @[Pending, Todo]
+
+    for s in futureCategories:
       if ctx.issues.hasKey(s) and ctx.issues[s].len > 0:
         let visibleIssues = ctx.issues[s].filterIt(
           showHidden or