Allow filtering by remote addresses (#52)

* Added the possibility to define rules for remote addresses

* Added change in changelog

* Added check for X-Real-Ip and X-Forwarded-For when checking for remote address filtering

* cmd/anubis: refine IP filtering logic

* Optimize the configuration so that the IP trie is created once at
  application start instead of dynamically being created every request.
* Document the changes in the changelog and docs site.
* Allow pure IP range filtering.
* Allow user agent based IP range filtering.
* Allow path based IP range filtering.
* Create --debug-x-real-ip-default flag for testing Anubis locally
  without a HTTP load balancer.

---------

Co-authored-by: Xe Iaso <me@xeiaso.net>

cmd/anubis/internal/config/testdata/good/allow_everyone.json

@@ -0,0 +1,12 @@
+{
+  "bots": [
+    {
+      "name": "everyones-invited",
+      "remote_addresses": [
+        "0.0.0.0/0",
+        "::/0"
+      ],
+      "action": "ALLOW"
+    }
+  ]
+}