Feat: Add support for gpt-4 models (#157)

completion.go

@@ -17,6 +17,10 @@ var (
 // GPT3 Models are designed for text-based tasks. For code-specific
 // tasks, please refer to the Codex series of models.
 const (
+	GPT432K0314             = "gpt-4-32k-0314"
+	GPT432K                 = "gpt-4-32k"
+	GPT40314                = "gpt-4-0314"
+	GPT4                    = "gpt-4"
 	GPT3Dot5Turbo0301       = "gpt-3.5-turbo-0301"
 	GPT3Dot5Turbo           = "gpt-3.5-turbo"
 	GPT3TextDavinci003      = "text-davinci-003"