message: Add Default to structs
  This has minimal implications on total code size, bumping it by
  about 2%
diff: @@ -119,7 +119,7 @@ fn main() -> Result<()> {
  meta.schema_to_id_type(schema).unwrap_or_else(|| ("()".into(), CopyOrClone::Copy));
  let struct_type = meta.schema_to_rust_type(schema);
  out.push_str(&format!("#[cfg(not(feature = \"{}\"))]\n", feature));
  - out.push_str("#[derive(Clone, Debug, Deserialize, Serialize)]\n");
  + out.push_str("#[derive(Clone, Debug, Default, Deserialize, Serialize)]\n");
  out.push_str(&format!("pub struct {} {{\n", struct_type));
  out.push_str(&format!("\tpub id: {},\n", id_type));
  out.push_str("}\n\n");
  @@ -380,7 +380,7 @@ fn gen_struct(
  out.push_str(&doc_url);
  out.push_str(">\n");
  }
  - out.push_str("#[derive(Clone, Debug, Deserialize, Serialize)]\n");
  + out.push_str("#[derive(Clone, Debug, Default, Deserialize, Serialize)]\n");
  out.push_str("pub struct ");
  out.push_str(&struct_name);
  out.push_str(" {\n");
  @@ -511,7 +511,7 @@ fn gen_generated_schemas(
  {
  let struct_name = meta.schema_to_rust_type(&schema_name);
  out.push('\n');
  - out.push_str("#[derive(Clone, Debug, Deserialize, Serialize)]\n");
  + out.push_str("#[derive(Clone, Debug, Default, Deserialize, Serialize)]\n");
  out.push_str("pub struct ");
  out.push_str(&struct_name);
  out.push_str(" {\n");
  @@ -1084,7 +1084,7 @@ fn gen_emitted_structs(
  }
  };
  out.push('\n');
  - out.push_str("#[derive(Clone, Debug, Deserialize, Serialize)]\n");
  + out.push_str("#[derive(Clone, Debug, Default, Deserialize, Serialize)]\n");
  out.push_str("pub struct ");
  out.push_str(&struct_name.to_camel_case());
  out.push_str(" {\n");
  