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

---------

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

examples/query_segments_demo/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "query_segments_demo"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+dioxus = { path = "../../packages/dioxus", version = "*" }
+dioxus-router = { path = "../../packages/router", version = "*" }
+dioxus-web = { path = "../../packages/web", version = "*" }
+form_urlencoded = "1.2.0"