Improve logging (#31)

* Add more debug logging

* Set default logging to `info`

src/mail.rs

@@ -48,6 +48,8 @@ pub fn send(topic: &Topic, posts: &Posts, expression: &str, config: &Config) {
         .add_subject(&topic.title)
         .add_html(&html_message);
 
+    debug!("Sending email notification.");
+
     match sg.send(mail_info) {
         Err(err) => println!("SendGrid failed to send mail. Error: {}", err),
         Ok(body) => println!("SendGrid Response: {:?}", body),