Doc: update maintenance document

maintenance.md

@@ -29,25 +29,41 @@
 - Get announcement from Github file
 - Support multiple connections in custom ovpn
 
+## Gluetun pre-v4
+
+- Finish HTTP server v1 or v2
+- Renamings
+  - `UNBLOCK` to `DOT_UNBOUND_UNBLOCK`
+  - `PIA_ENCRYPTION` to `PRIVATE_INTERNET_ACCESS_OPENVPN_ENCRYPTION_PRESET`
+  - `PORT_FORWARDING` to `PRIVATE_INTERNET_ACCESS_VPN_PORT_FORWARDING`
+  - Rename PIA's `REGION` to `COUNTRY`
+  - `WIREGUARD_ADDRESS` to `WIREGUARD_ADDRESSES`
+  - `VPNSP` to `VPN_SERVICE_PROVIDER`
+  - Rename `REGION` (etc.) to `SERVER_REGIONS`
+- Split servers.json and compress it
+
 ## Gluetun V4
 
-- Remove retro environment variables
+- Remove retro environment variables:
+  - `PORT`
+  - `UNBLOCK`
+  - `PROTOCOL`
+  - `PIA_ENCRYPTION`
+  - `PORT_FORWARDING`
+  - `WIREGUARD_PORT`
+  - `REGION` for PIA
+  - `WIREGUARD_ADDRESS`
+  - `VPNSP`
+  - All old location filters such as `REGION`, `COUNTRY`, etc.
+- Remove other retro logic
+  - `VPNSP`'s `pia = private ...`
+  - Remove `OPENVPN_CONFIG` != "" implies `VPNSP` = "custom" AND set `OPENVPN_CUSTOM_CONFIG` default to `/gluetun/custom.ovpn`
+- Remove functionalities
+  - `SERVER_NUMBER`
+  - `PUBLICIP_FILE`
+  - `PORT_FORWARDING_STATUS_FILE`
 - Updater servers version reset to 1
-- Change models to all have IPs instead of IP
 - Remove HTTP server v0
-- `PORT` to `OPENVPN_PORT`
-- `UNBLOCK` to `DOT_UNBOUND_UNBLOCK`
-- Remove `PROTOCOL`
-- `PORT_FORWARDING`
-- Change servers filtering environment variables to plural
-- Remove `WIREGUARD_PORT`
-- `WIREGUARD_ADDRESS` to `WIREGUARD_ADDRESSES`
-- Only use `custom` VPNSP for custom OpenVPN configurations
-- `VPNSP` compulsory
-- Change `VPNSP` to `VPN_SERVICE_PROVIDER`
-- Change `REGION` (etc.) to `SERVER_REGIONS`
-- Remove `PUBLICIP_FILE`
-- Remove retro-compatibility where OPENVPN_CONFIG != "" implies VPNSP = "custom"
- and set `OPENVPN_CUSTOM_CONFIG` default to `/gluetun/custom.ovpn`
-- Split servers.json and compress it
+- Change to compulsory
+  - `VPN_SERVICE_PROVIDER`
 - Use relative paths everywhere instead of absolute