Patched Sanitizer: Added h4, h5, h6 to the whitelist

```
sanitizeTag was removing the h4, h5 and h6 because they weren't in the
`basic_tag_whitelist`, so I added them.
```

Original issue reported on code.google.com by `r...@rodyhaddad.com` on 16 May 2013 at 3:35

Attachments:
- [Markdown.Sanitizer.js.patch](https://storage.googleapis.com/google-code-attachments/pagedown/issue-58/comment-0/Markdown.Sanitizer.js.patch)

修補檔案顯示了確切的變更：將 'h4'、'h5'、'h6' 新增至 Markdown.Sanitizer.js 中的 basic_tag_whitelist。找到該檔案、套用修補程式，並測試清理程序不再移除這些標題標籤。不過，這個 issue 來自 2013 年，近期沒有活動，因此請檢查專案是否仍接受修補程式。

由索引模型根據 Issue 內容生成。