Updated changelog and added scare message to the list_clipper.

CHANGELOG.markdown

@@ -51,6 +51,11 @@
 - The variants of `ColorEditInputMode` and `ColorEditDisplayMode` have been renamed to be CamelCase instead of upper case (e.g. `ColorEditFooMode::RGB` => `ColorEditFooMode::Rgb`).
     - However, this change is probably not breaking (in practice if not in theory) because const aliases using the old names are provided.
 
+- Most tokens through the repository (eg. `WindowToken`, `TabBarToken`, `FontStackToken`, etc) now allow for permissive dropping -- i.e, you don't need to actually call the `.end()` method on them anymore. In exchange, these tokens have taken on a lifetime, which allows them to be safe.
+- `end()` no longer takes `Ui`. This is a breaking change, but hopefully should be trivial (and perhaps nice) for users to fix. Simply delete the parameters, or add a `_` before the token's binding name and allow it to be dropped on its own.
+
+- `PopupModal`'s `new` was reworked so that it didn't take `Ui` until `build` was called. This is a breaking change if you were invoking it directly. Simply move your `ui` call to `build` or `begin`.
+
 ## [0.6.1] - 2020-12-16
 
 - Support for winit 0.24.x

imgui/src/list_clipper.rs

@@ -71,7 +71,11 @@ impl<'ui> Drop for ListClipperToken<'ui> {
                 sys::ImGuiListClipper_destroy(self.list_clipper);
             };
         } else if !thread::panicking() {
-            panic!("Forgot to call End(), or to Step() until false?");
+            panic!(
+                "Forgot to call End(), or to Step() until false? \
+            This is the only token in the repository which users must call `.end()` or `.step()` \
+            with. See https://github.com/imgui-rs/imgui-rs/issues/438"
+            );
         }
     }
 }