Support gpt 3.5 turbo 16k model

`TokenLimits` is only the place needed to be modified. Have set the token limits accordingly.

Author: HyunggyuJang

src/limits.ts

@@ -9,6 +9,9 @@ export class TokenLimits {
     if (model === 'gpt-4-32k') {
       this.maxTokens = 32600
       this.responseTokens = 4000
+    if (model === 'gpt-3.5-turbo-16k') {
+      this.maxTokens = 16300
+      this.responseTokens = 3000
     } else if (model === 'gpt-4') {
       this.maxTokens = 8000
       this.responseTokens = 2000