Move AstNode into the types crate.

Now that it is used for more than just iteration, it makes sense to promote it to the types crate.

src/parser/document.rs

@@ -20,7 +20,7 @@ use crate::context::RefContext;
 use crate::error::CustomError;
 use crate::error::MyError;
 use crate::error::Res;
-use crate::iter::AstNode;
+use crate::types::AstNode;
 use crate::parser::org_source::convert_error;
 use crate::parser::util::blank_line;
 use crate::types::Document;

src/parser/in_buffer_settings.rs

@@ -11,7 +11,7 @@ use super::OrgSource;
 use crate::context::HeadlineLevelFilter;
 use crate::error::CustomError;
 use crate::error::Res;
-use crate::iter::AstNode;
+use crate::types::AstNode;
 use crate::settings::GlobalSettings;
 use crate::types::Document;
 use crate::types::Keyword;