feat: Adds section and section style, needs tests

Sources/CliDoc/Modifiers/SectionStyle.swift

@@ -0,0 +1,37 @@
+public extension Section {
+
+  @inlinable
+  func style<S: SectionStyle>(_ style: S) -> some TextNode {
+    style.render(content: .init(header: header, content: content, footer: footer))
+  }
+}
+
+public struct SectionConfiguration {
+  public let header: any TextNode
+  public let content: any TextNode
+  public let footer: any TextNode
+
+  @usableFromInline
+  init(header: any TextNode, content: any TextNode, footer: any TextNode) {
+    self.header = header
+    self.content = content
+    self.footer = footer
+  }
+}
+
+public protocol SectionStyle: NodeModifier where Content == SectionConfiguration {}
+
+public extension SectionStyle where Self == DefaultSectionStyle {
+  static var `default`: Self { DefaultSectionStyle() }
+}
+
+public struct DefaultSectionStyle: SectionStyle {
+
+  public func render(content: SectionConfiguration) -> some TextNode {
+    VStack {
+      content.header
+      content.content
+      content.footer.textStyle(.italic)
+    }
+  }
+}