Working apalis cron and worker with 0.6.0-rc.5

Also renamed `pool` variables throughout codebase to `db` for clarity.

src/jobs/crawl_feed.rs

@@ -0,0 +1,8 @@
+use serde::{Deserialize, Serialize};
+
+use crate::models::feed::Feed;
+
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct CrawlFeedJob {
+    pub feed: Feed,
+}