Can build indexes on new columns

storage_engine/src/storage_engine.rs

@@ -184,9 +184,16 @@ impl <T>Store<T> {
         WriteCursor::new(self).await
     }
 
-    pub async fn make_indexable(&mut self, column: Column) -> Result<()> {
-        // Creates an index from scratch at above column
-        todo!()
+    // ===Indexes===
+    pub async fn attach_index(&mut self, column: Column) -> Result<()> 
+        where T: Ord + Decode + Encode + Send + Sync
+    {
+        if self.header.is_column_indexed(column) {
+            Err(Error::ColumnAlreadyIndexed(column))
+        } else {
+            let mut cursor = self.write_cursor().await?;
+            cursor.attach_index(column).await
+        }
     }
 
     // For debugging.