Adds support for Anthropic's messages API

[svs]

I saw @obie's PR and improved on it slightly.

• I removed the use of present? which is a Rails-only method so the library works outside of Rails as well
• I removed the retry logic which I believe should be a concern of the caller. This gem should faithfully report whatever Anthropic API returns
• I am also not a fan of having the messages function API break out the parameters. I understand it makes it marginally easier to call the API but there should also be a 1:1 mapping between the Anthropic API docs and our gem, which @obie's API breaks.
• I added a spec for the new method.

Hope this helps.

[deepakmahakale]

This is nice 👍

[deepakmahakale]

@alexrudall can we get this merged, please

[duncantmiller]

@alexrudall Looks great to me thanks for the work all!

[rameerez]

I've also tested this, works fine!

Thanks for the work, this makes it possible to use Claude 3, since the complete API was deprecated in favor of messages for the new models.

For future reference / Google, the error Anthropic throws when you try to use Claude 3 on the complete API is this:

{"type"=>"error", "error"=>{"type"=>"invalid_request_error", "message"=>"\"claude-3-opus-20240229\" is not supported on this API. Please use the Messages API instead."}}

[frmsaul]

Looks great! Thanks so much

[frmsaul]

We should probably update the README as well.

[deepakmahakale]

@alexrudall I have added documentation for messages API in this PR - https://github.com/alexrudall/anthropic/pull/12

We can merge #12 once this pr is merged

[Maclenn77]

I'm using this branch for a project, it's working well.

[drnic]

We should probably update the README as well.

Yep, let's get claude-3 + messages to top of README.

[drnic]

@alexrudall perhaps make some other people maintainers/gem releases?

[andreibondarev]

Let's ship this! 🚢 😄

[bloolizard]

nice can you guys merge this in!

[alexrudall]

Released in v0.2 - thanks all for your contributions, esp @obie and @svs !