Add OpenRouter support

[alr86]

When I use openrouter API as OpenAI, with every message app says:

Error: Illegal input: Unexpected JSON token at offset 9: Expected start of the object '{', but had '"' instead at path: $.error
JSON input: {"error":"Not Found"}

[Taewan-P]

@alr86 Check if your custom API address is correctly set. It should be like this: #62 (comment)

[alr86]

Thank you for your response.
I was using ‍https://openrouter.ai/api/v1/chat/completions, but the correct one is https://openrouter.ai/api/v1/.