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/iter/macros.rs

@@ -1,16 +1,3 @@
-/// Write the implementation of From<> to convert a borrow of the type to an AstNode
-macro_rules! to_ast_node {
-    ($inp:ty, $enum:expr) => {
-        impl<'r, 's> From<$inp> for AstNode<'r, 's> {
-            fn from(value: $inp) -> Self {
-                $enum(value)
-            }
-        }
-    };
-}
-
-pub(crate) use to_ast_node;
-
 /// Create iterators for ast nodes where it only has to iterate over children
 macro_rules! children_iter {
     ($astnodetype:ty, $itertype:ident, $innertype:ty) => {