Format transaction amounts on output

This might want to use the same YNAB CSV format as `convert`.

src/main.rs

@@ -171,7 +171,7 @@ async fn main() -> anyhow::Result<()> {
             };
             println!("Transactions{} in the last 30 days:", accountstr);
             for t in transactions {
-                println!("{},{},{}", t.date, t.payee, t.amount);
+                println!("{},{},{}", t.date, t.payee, t.format_amount());
             }
 
             Ok(())

src/transaction.rs

@@ -32,7 +32,7 @@ impl Transaction {
         })
     }
 
-    fn format_amount(&self) -> String {
+    pub fn format_amount(&self) -> String {
         let whole = self.amount / 10 / 100;
         let frac = if self.amount < 0 { -1 } else { 1 } * (self.amount / 10) % 100;
         format!("{}.{:02}", whole, frac)