added homework and atachments

src/attachment.rs

@@ -0,0 +1,10 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "PascalCase")]
+pub struct Attachment {
+    id: String,
+    name: String,
+    r#type: String,
+    size: u64,
+}