feat: Adds section and section style, needs tests

Sources/CliDoc/Nodes/Section.swift

@@ -0,0 +1,46 @@
+public struct Section<Header: TextNode, Content: TextNode, Footer: TextNode>: TextNode {
+
+  @usableFromInline
+  let header: Header
+
+  @usableFromInline
+  let content: Content
+
+  @usableFromInline
+  let footer: Footer
+
+  @inlinable
+  public init(
+    @TextBuilder header: () -> Header,
+    @TextBuilder content: () -> Content,
+    @TextBuilder footer: () -> Footer
+  ) {
+    self.header = header()
+    self.content = content()
+    self.footer = footer()
+  }
+
+  public var body: some TextNode {
+    style(.default)
+  }
+}
+
+public extension Section where Footer == Empty {
+  @inlinable
+  init(
+    @TextBuilder header: () -> Header,
+    @TextBuilder content: () -> Content
+  ) {
+    self.init(header: header, content: content) { Empty() }
+  }
+}
+
+public extension Section where Header == Empty {
+  @inlinable
+  init(
+    @TextBuilder content: () -> Content,
+    @TextBuilder footer: () -> Footer
+  ) {
+    self.init(header: { Empty() }, content: content, footer: footer)
+  }
+}