Add Google AI provider

[suizideFloat]

Would love to see Google Gemini as a provider for this great project, as it is a very powerful LLM and has even good free availability and rate limits.

[djcopley]

Thanks for the suggestion! Do you have a particular model you'd like to see as the default?

[lpgn]

Initial Gemini integration (gemini-pro) implemented.
my commit d6e102e

[djcopley]

Thanks @lpgn! Gemini will be in the next release.