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
.

.

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db/stats.sql

@@ -0,0 +1,5 @@
+SELECT
+    COUNT(CASE WHEN response_code IS NOT NULL AND error IS NULL THEN 1 END) AS "Visited",
+    COUNT(CASE WHEN response_code IS NULL THEN 1 END) AS "Pending",
+    COUNT(CASE WHEN error IS NOT NULL THEN 1 END) AS "Errors"
+FROM snapshots;