add filter_private_ips option to discard private IPs.

Might be used when tracker is behind reverse proxy and one of provided
addresses in `real_ip_header` is private/local address.

Additional changes:

* check if provided address is not multicast/broadcast
* configure `http.Server.ReadHeaderTimeout` with `http.ReadTimeout` to mitigate Slowloris
* update dependencies
* minor docs fixes

docs/frontend.md

@@ -50,7 +50,7 @@ The typical control flow of handling announces, in more detail, is:
 #### Configuration
 
 The frontend must be configurable using a single, exported struct. The struct must have YAML annotations. The struct
-must implement `log.Fielder` to be logged on startup.
+must implement `zerolog.LogObjectMarshaler` to be logged on startup.
 
 #### Metrics
 

docs/storage/postgres.md

@@ -116,7 +116,7 @@ storage:
             graduate_query: UPDATE mo_peers SET is_seeder=TRUE WHERE info_hash=$1 AND peer_id=$2 AND address=$3 AND port=$4 AND NOT is_seeder
             # Query to get count of peers.
             # Used both for statistics and for scrape (with clause suffix, see next).
-            # Only first returned row values used.
+            # Only first returned row value used.
             count_query: SELECT COUNT(1) FILTER (WHERE is_seeder) AS seeders, COUNT(1) FILTER (WHERE NOT is_seeder) AS leechers FROM mo_peers
             # Predicate part of `count_query` for get count of peers by info hash
             by_info_hash_clause: WHERE info_hash = $1