createCompletion method returning 404 for 'code-davinci-003' model

[ben-elliot-nice]

Was reading here that you should now use the gtp models and the createChatCompletion method instead of createCompletion.

If I find time I will write and submit a PR to fix.

Also, the version published on the VSCode Extension store is the old version (not 2.0.0), so to get the current version you need to install from the github repo.