Implemented disallow_unknown

* Added codegen for disallow_unknown
* ... with new default to ignore unknown values during deserialization
* Added ContainerAttrs

serde_codegen/src/field.rs

@@ -2,7 +2,7 @@ use syntax::ast;
 use syntax::ext::base::ExtCtxt;
 
 use aster;
-use attr::{FieldAttrs, FieldAttrsBuilder};
+use attr::{ContainerAttrs, ContainerAttrsBuilder, FieldAttrs, FieldAttrsBuilder};
 
 pub fn struct_field_attrs(
     _cx: &ExtCtxt,
@@ -15,3 +15,10 @@ pub fn struct_field_attrs(
         })
         .collect()
 }
+
+pub fn container_attrs(
+    _cx: &ExtCtxt,
+    container: &ast::Item,
+) -> ContainerAttrs {
+    ContainerAttrsBuilder::new().attrs(container.attrs()).build()
+}