Add the rest of the Chat Completion fields (#92)

Per https://platform.openai.com/docs/api-reference/chat/create

chat.go

@@ -21,6 +21,16 @@ type ChatCompletionMessage struct {
 type ChatCompletionRequest struct {
 	Model            string                  `json:"model"`
 	Messages         []ChatCompletionMessage `json:"messages"`
+	MaxTokens        int                     `json:"max_tokens,omitempty"`
+	Temperature      float32                 `json:"temperature,omitempty"`
+	TopP             float32                 `json:"top_p,omitempty"`
+	N                int                     `json:"n,omitempty"`
+	Stream           bool                    `json:"stream,omitempty"`
+	Stop             []string                `json:"stop,omitempty"`
+	PresencePenalty  float32                 `json:"presence_penalty,omitempty"`
+	FrequencyPenalty float32                 `json:"frequency_penalty,omitempty"`
+	LogitBias        map[string]int          `json:"logit_bias,omitempty"`
+	User             string                  `json:"user,omitempty"`
 }
 
 type ChatCompletionChoice struct {