Make a few helper functions and values public. (#6)

* Make a few helper functions and values public.

* More escaping helpers.

Sources/Html/Render.swift

@@ -11,17 +11,17 @@ public func render(_ nodes: [Node]) -> String {
 public func render(_ node: Node) -> String {
   switch node {
   case let .comment(string):
-    return "<!-- \(string.replacingOccurrences(of: "-->", with: "--&gt;")) -->"
+    return "<!-- \(escapeHtmlComment(string)) -->"
   case let .doctype(string):
-    return "<!DOCTYPE \(string.replacingOccurrences(of: ">", with: "&gt;"))>"
+    return "<!DOCTYPE \(escapeDoctype(string))>"
   case let .element(tag, attribs, children):
     let renderedAttribs = render(attribs)
     guard !children.isEmpty else {
       return "<" + tag + renderedAttribs + (voidElements.contains(tag) ? ">" : "/>")
     }
     return "<" + tag + renderedAttribs + ">" + render(children) + "</" + tag + ">"
   case let .text(string):
-    return escape(html: string)
+    return escapeTextNode(text: string)
   case let .raw(string):
     return string
   }
@@ -39,20 +39,32 @@ private func render(_ attribs: [(String, String?)]) -> String {
   return attribs
     .compactMap { key, value in
       value.map {
-        " " + key + ($0.isEmpty ? "" : "=\"\($0.replacingOccurrences(of: "\"", with: "&quot;"))\"")
+        " " + key + ($0.isEmpty ? "" : "=\"\(escapeAttributeValue($0))\"")
       }
     }
     .joined()
 }
 
-private func escape(html: String) -> String {
-  return html
+public func escapeAttributeValue(_ value: String) -> String {
+  return value.replacingOccurrences(of: "\"", with: "&quot;")
+}
+
+public func escapeTextNode(text: String) -> String {
+  return text
     .replacingOccurrences(of: "&", with: "&amp;")
     .replacingOccurrences(of: "<", with: "&lt;")
 }
 
+public func escapeDoctype(_ doctype: String) -> String {
+  return doctype.replacingOccurrences(of: ">", with: "&gt;")
+}
+
+public func escapeHtmlComment(_ comment: String) -> String {
+  return comment.replacingOccurrences(of: "-->", with: "--&gt;")
+}
+
 /// A set of self-closing "void" elements that should not contain child nodes.
-private let voidElements: Set<String> = [
+public let voidElements: Set<String> = [
   "area",
   "base",
   "br",