Add --post-count option

src/main.rs

@@ -82,7 +82,9 @@ async fn main() -> Result<()> {
     let reddit_client = RedditClient::new();
     let mut user_posts = MultiMap::new();
     for username in unique_usernames {
-        let submissions = reddit_client.fetch_user_submissions(&username).await?;
+        let submissions = reddit_client
+            .fetch_user_submissions(&username, args.post_count)
+            .await?;
         user_posts.insert_many(username, submissions);
     }