0.2.0

Features:

• added integration tests for max_tokens and stop sequence parameters (#23)
• allowed empty messages in each language model (#23)
• supported history truncation via max_prompt_tokens and discarded_messages parameters (#23)
• supported streaming for Titan and Claude (#23)

Fixes:

• used number of bytes as token count estimator for AI21 and AWS Titan (#23)
• fixed AI21 temperature setting (#23)
• removed Assistant prefix occasionally generated by Titan (#23)