Lots of features, first version that reliably crawls Geminispace.

- [x] Concurrent downloading with workers
- [x] Concurrent connection limit per host
- [x] URL Blacklist
- [x] Save image/* and text/* files
- [x] Configuration via environment variables
- [x] Storing snapshots in PostgreSQL
- [x] Proper response header & body UTF-8 and format validation
.

.

db/show-dups.sql

@@ -0,0 +1,9 @@
+WITH DuplicateSnapshots AS (
+    SELECT id,
+           url,
+           ROW_NUMBER() OVER (PARTITION BY url ORDER BY id) AS row_num
+    FROM snapshots
+)
+SELECT *
+FROM DuplicateSnapshots
+WHERE row_num > 1;