Add tests and a Sizable trait for ContextElement.

src/renderer/parameters_context.rs

@@ -14,6 +14,7 @@ use crate::renderer::DustRenderer;
 use crate::renderer::Loopable;
 use crate::renderer::RenderError;
 use crate::renderer::Renderable;
+use crate::renderer::Sizable;
 use crate::renderer::Truthiness;
 use crate::renderer::WalkError;
 use crate::renderer::Walkable;
@@ -189,6 +190,12 @@ impl Walkable for OwnedLiteral {
     }
 }
 
+impl Sizable for OwnedLiteral {
+    fn get_size<'a>(&'a self) -> Option<IceResult<'a>> {
+        todo!()
+    }
+}
+
 impl Castable for OwnedLiteral {
     fn cast_to_type<'a>(&'a self, target: &str) -> Option<IceResult<'a>> {
         match (self, target) {