Rework Guide (#486)

* Move getting started to Guide

* Clean up summary and getting started

* Shorten intro by moving stuff to individual platform docs

* Make intro even shorter, summarize features

* Further cleanup; move development-related docs to separate section

* Make `guide` a crate. Turn code samples into examples so that we can check if they compile

* Rewrite "Describing the UI":

* Focus on RSX syntax (interactivity covered in later chapters); make sure samples are tested; concise language

* Move some "special attribute" samples to the `examples` directory

* Simplify introduction to components

* Simplify introduction to component props

* Document Prop features; add code samples

* Simplify component children docs

* Interactivity: better introduction to events

* Hooks: better introduction

* Remove outdated doc

* Introducs use_ref

* Simplify User Input chapter

* Document event handler props

* Meme editor example

* Meme editor walkthrough

* Add dark mode example

* Guide for context; dark mode example

* Guide: custom hooks

* Guide: conditional rendering

* Guide: rendering lists

* Guide: rendering lists + keys

* Move remaining infor from Reference to guide

* Delete reference book

docs/guide/examples/component_props_options.rs

@@ -0,0 +1,113 @@
+#![allow(non_snake_case)]
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::desktop::launch(App);
+}
+
+fn App(cx: Scope) -> Element {
+    cx.render(rsx! {
+        // ANCHOR: OptionalProps_usage
+        Title {
+            title: "Some Title",
+        },
+        Title {
+            title: "Some Title",
+            subtitle: "Some Subtitle",
+        },
+        // Providing an Option explicitly won't compile though:
+        // Title {
+        //     title: "Some Title",
+        //     subtitle: None,
+        // },
+        // ANCHOR_END: OptionalProps_usage
+
+        // ANCHOR: ExplicitOption_usage
+        ExplicitOption {
+            title: "Some Title",
+            subtitle: None,
+        },
+        ExplicitOption {
+            title: "Some Title",
+            subtitle: Some("Some Title"),
+        },
+        // This won't compile:
+        // ExplicitOption {
+        //     title: "Some Title",
+        // },
+        // ANCHOR_END: ExplicitOption_usage
+
+        // ANCHOR: DefaultComponent_usage
+        DefaultComponent {
+            number: 5,
+        },
+        DefaultComponent {},
+        // ANCHOR_END: DefaultComponent_usage
+
+        // ANCHOR: IntoComponent_usage
+        IntoComponent {
+            string: "some &str",
+        },
+        // ANCHOR_END: IntoComponent_usage
+    })
+}
+
+// ANCHOR: OptionalProps
+#[derive(Props)]
+struct OptionalProps<'a> {
+    title: &'a str,
+    subtitle: Option<&'a str>,
+}
+
+fn Title<'a>(cx: Scope<'a, OptionalProps>) -> Element<'a> {
+    return cx.render(rsx!(h1{
+        "{cx.props.title}: ",
+        [cx.props.subtitle.unwrap_or("No subtitle provided")],
+    }));
+}
+// ANCHOR_END: OptionalProps
+
+// ANCHOR: ExplicitOption
+#[derive(Props)]
+struct ExplicitOptionProps<'a> {
+    title: &'a str,
+    #[props(!optional)]
+    subtitle: Option<&'a str>,
+}
+
+fn ExplicitOption<'a>(cx: Scope<'a, ExplicitOptionProps>) -> Element<'a> {
+    return cx.render(rsx!(h1{
+        "{cx.props.title}: ",
+        [cx.props.subtitle.unwrap_or("No subtitle provided")],
+    }));
+}
+// ANCHOR_END: ExplicitOption
+
+// ANCHOR: DefaultComponent
+#[derive(PartialEq, Props)]
+struct DefaultProps {
+    // default to 42 when not provided
+    #[props(default = 42)]
+    number: i64,
+}
+
+fn DefaultComponent(cx: Scope<DefaultProps>) -> Element {
+    return cx.render(rsx!(h1{
+        "{cx.props.number}",
+    }));
+}
+// ANCHOR_END: DefaultComponent
+
+// ANCHOR: IntoComponent
+#[derive(PartialEq, Props)]
+struct IntoProps {
+    #[props(into)]
+    string: String,
+}
+
+fn IntoComponent(cx: Scope<IntoProps>) -> Element {
+    return cx.render(rsx!(h1{
+        "{cx.props.string}",
+    }));
+}
+// ANCHOR_END: IntoComponent