Add api documentation by using swifts docc (#94)

* Bump the minimum swift version to 5.6

* Add swifts docc to document the api

* Remove the old instructions

* Add articles to the documentation catalog

* Add a manifest file for swiftpackageindex

* Remove script files

.spi.yml

@@ -0,0 +1,4 @@
+version: 1
+builder:
+  configs:
+    - documentation_targets: [HTMLKit]

Package.swift

@@ -1,5 +1,4 @@
-// swift-tools-version:5.4
-// The swift-tools-version declares the minimum version of Swift required to build this package.
+// swift-tools-version:5.6
 
 import PackageDescription
 
@@ -17,6 +16,7 @@ let package = Package(
     dependencies: [
         .package(url: "https://github.com/miroslavkovac/Lingo.git", from: "3.1.0"),
         .package(url: "https://github.com/apple/swift-collections.git", from: "1.0.1"),
+        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0")
     ],
     targets: [
         .target(

Sources/HTMLKit/Documentation.docc/Essentials/Getting_started.md

@@ -0,0 +1,42 @@
+# Getting started
+
+Learn how to use it.
+
+### Requirements
+
+HTMLKit requires Swift 5.6 or higher.
+
+### Installation
+
+To use HTMLKit in your project, you have to add the package as dependency to your package description first. Be sure to add it as your desired targets as well.
+
+```swift
+let package = Package(
+    ...
+    dependencies: [
+        // 1. Add the package
+        .package(url: "https://github.com/vapor-community/HTMLKit.git", from: "2.6.0"),
+    ],
+    targets: [
+        .target(
+            ...
+            dependencies: [
+                /// 2. Add the product
+                .product(name: "HTMLKit", package: "HTMLKit"),
+            ]
+        ),
+        ...
+    ]
+)
+```
+
+From time to time you want to update the package. You can do it, by changing the version tag manually and saving it. You find the current version tag in the [release history](https://github.com/vapor-community/HTMLKit/releases). We recommand to read the release description first, to understand the possible changes.
+
+### Usage
+
+Use the import keyword to load the module in your project files.
+
+```swift
+import HTMLKit
+...
+```

Instructions/Essential/Context.md → Sources/HTMLKit/Documentation.docc/Essentials/Parts/Context.md

@@ -1,14 +1,8 @@
 # Context
 
-The context is
-
-## Essential
-
-### Definition
+## Overview
 
 ```swift
-/// [SimpleContext.swift]
-
 struct SimpleContext: Codable {
 
     var headline: String
@@ -17,8 +11,6 @@ struct SimpleContext: Codable {
 ```
 
 ```swift
-/// [SimpleView.swift]
-
 struct SimpleView: View {
 
     @TemplateValue(SimpleContext.self)

Instructions/Essential/Elements.md → Sources/HTMLKit/Documentation.docc/Essentials/Parts/Elements.md

@@ -1,8 +1,8 @@
 # Elements
 
-The elements in HTMLKit represent the official HTML elements. Elements with content use the curly brackets, while elements without content use the round brackets. To add attributes to the element use the offered functions.
+## Overview
 
-## Essential
+The elements in HTMLKit represent the official HTML elements. Elements with content use the curly brackets, while elements without content use the round brackets. To add attributes to the element use the offered functions.
 
 ### Definition
 
@@ -50,8 +50,6 @@ Body {
 To prevent invalid code, each element owns a element definition. For example the element `Heading1` is a type of `BodyElement`, so it is only allowed to be placed in the `Body` element. See the [wiki](https://github.com/vapor-community/HTMLKit/wiki) for more element definitions.
 
 ```swift
-/// [BodyElements.swift]
-
 public struct Heading1: ContentNode, BodyElement {
     ...
 }

Instructions/Essential/Layouts.md → Sources/HTMLKit/Documentation.docc/Essentials/Parts/Layouts.md

@@ -1,16 +1,14 @@
 # Layouts
 
+## Overview
+
 Layouts allow to define a website template. It is used to provide a consistend look.
 
 ## Page
 
 The page is the entry point of the site. It should be used to package the views.
 
-### Definition
-
 ```swift
-/// [SimplePage.swift]
-
 struct SimplePage: Page {
 
     var body: AnyContent {
@@ -32,11 +30,7 @@ struct SimplePage: Page {
 
 The view is a partial view of the page. It should be used to display data using the context.
 
-### Definition
-
 ```swift
-/// [SimpleView.swift]
-
 struct SimpleView: View {
 
     @TemplateValue(SimpleContext.self)
@@ -50,19 +44,13 @@ struct SimpleView: View {
 }
 ```
 
-### Context
-
 The context as an object holds the information for the view. ... See [Context](https://github.com/vapor-community/HTMLKit/blob/master/Instructions/Essential/Context.md) to learn more about it.
 
 ## Component
 
 The component is a reusable portion of a page. It should be used to break up large files into smaller components.
 
-### Definition
-
 ```swift
-/// [SimpleComponent.swift]
-
 struct SimpleComponent: Component {
 
     var body: AnyContent {