Server script to download the latest installer

As promised, I talked with enumag about the script and he sent it to me earlier today.

You can access it at http://07th-mod.com/installer.php

By default, it will guess the user platform and get the latest stable release. You can force it to go through manually using: ``http://07th-mod.com/installer.php?system=win|mac|linux&branch=pre|stable``

Example: http://07th-mod.com/installer.php?system=linux&branch=stable

Beware that using ``branch=pre`` will only work if the most recent release is marked as a pre-release. If the most recent is a stable release, it will get the stable instead of the pre-release.

Right now the guessing part doesn't work, but I believe it is because of the current changes ongoing at the releases page. Earlier today it was working fine, so it might fix itself soon enough.

該腳本託管在 http://07th-mod.com/installer.php 並與 GitHub 發佈版本互動。首先檢查現有的伺服器端邏輯，用於平台檢測和發佈版本獲取。了解它如何確定 'stable' 與 'pre' 分支，並與專案的發佈頁面整合。使用不同的查詢參數測試端點，以驗證目前行為並識別猜測問題。

由索引模型根據 Issue 內容生成。