Create structure for footnote references.

src/parser/mod.rs

@@ -12,6 +12,7 @@ mod exiting;
 mod export_snippet;
 mod fixed_width_area;
 mod footnote_definition;
+mod footnote_reference;
 mod greater_block;
 mod greater_element;
 mod horizontal_rule;
@@ -75,6 +76,7 @@ pub use object::Bold;
 pub use object::Code;
 pub use object::Entity;
 pub use object::ExportSnippet;
+pub use object::FootnoteReference;
 pub use object::Italic;
 pub use object::LatexFragment;
 pub use object::Object;