Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibHTML/DOM/Node.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <AK/Badge.h>
+#include <AK/RefPtr.h>
+#include <AK/Vector.h>
+#include <LibHTML/TreeNode.h>
+
+enum class NodeType : unsigned {
+    INVALID = 0,
+    ELEMENT_NODE = 1,
+    TEXT_NODE = 3,
+    DOCUMENT_NODE = 9,
+};
+
+class ParentNode;
+
+class Node : public TreeNode<Node> {
+public:
+    virtual ~Node();
+
+    NodeType type() const { return m_type; }
+    bool is_element() const { return type() == NodeType::ELEMENT_NODE; }
+    bool is_text() const { return type() == NodeType::TEXT_NODE; }
+    bool is_document() const { return type() == NodeType::DOCUMENT_NODE; }
+    bool is_parent_node() const { return is_element() || is_document(); }
+
+protected:
+    explicit Node(NodeType);
+
+    NodeType m_type { NodeType::INVALID };
+};