Add query segment example and documentation (#1417)

* fix a few new clippy lints

* Add query segment example

* Add trait documentation

* Change core package to root package

The core package contains the virtual dom implementation ([here](https://github.com/DioxusLabs/dioxus/tree/master/packages/core)). Root package might be a more clear way to refer to the main directory

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Co-authored-by: Evan Almloff <evanalmloff@gmail.com>

Cargo.toml

@@ -42,6 +42,7 @@ members = [
     # Full project examples
     "examples/tailwind",
     "examples/PWA-example",
+    "examples/query_segments_demo",
     # Playwright tests
     "playwright-tests/liveview",
     "playwright-tests/web",