Introduce the document structure.

src/parser/mod.rs

@@ -12,10 +12,10 @@ mod paragraph;
 mod parser_context;
 mod parser_with_context;
 mod plain_list;
+mod source;
 mod text;
 mod token;
 mod util;
-pub use document::document;
 type Context<'r, 's> = &'r parser_context::ContextTree<'r, 's>;
 pub use parser_context::ContextTree;
 pub use plain_list::item;