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>

docs/docs/CHANGELOG.md

@@ -40,6 +40,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [KagiBot](https://kagi.com/bot) is allowed through the filter [#44](https://github.com/TecharoHQ/anubis/pull/44)
 - Fixed hang when navigator.hardwareConcurrency is undefined
 - Support Unix domain sockets [#45](https://github.com/TecharoHQ/anubis/pull/45)
+- Allow filtering by remote addresses:
+
+  ```json
+  {
+    "name": "qwantbot",
+    "user_agent_regex": "\\+https\\:\\/\\/help\\.qwant\\.com/bot/",
+    "action": "ALLOW",
+    "remote_addresses": ["91.242.162.0/24"]
+  }
+  ```
+
+  This also works at an IP range level:
+
+  ```json
+  {
+    "name": "internal-network",
+    "action": "ALLOW",
+    "remote_addresses": ["100.64.0.0/10"]
+  }
+  ```
 
 ## 1.13.0