增加自定义 Prompts [Add Custom Prompts Support]

Poe过来的, Poe渲染太的实在太丑了, 但是自定义 Prompt 用着很不错, 希望可以支持一下, 就很完美了

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I came from Poe, and while Poe's rendering is quite ugly, the custom prompts feature is really nice. It would be perfect if you could support custom prompts as well.