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/Document.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <AK/AKString.h>
+#include <AK/NonnullRefPtrVector.h>
+#include <AK/OwnPtr.h>
+#include <LibHTML/CSS/StyleResolver.h>
+#include <LibHTML/CSS/StyleSheet.h>
+#include <LibHTML/DOM/ParentNode.h>
+
+class LayoutNode;
+class StyleResolver;
+class StyleSheet;
+
+class Document : public ParentNode {
+public:
+    Document();
+    virtual ~Document() override;
+
+    StyleResolver& style_resolver();
+
+    void add_sheet(const StyleSheet& sheet) { m_sheets.append(sheet); }
+    const NonnullRefPtrVector<StyleSheet>& stylesheets() const { return m_sheets; }
+
+private:
+    OwnPtr<StyleResolver> m_style_resolver;
+    NonnullRefPtrVector<StyleSheet> m_sheets;
+};