3.1.0 - CLI Save and Load commands

This release only changes the CLI. It adds the ability to save and load conversations, as requested by issue #3. To save your conversation, you'll need to specify it when launching the CLI:

# Generated timestamped name
gpt-turbo --save

# Custom name
gpt-turbo --save my-conversation

Then load it at a later time

gpt-tubo --load ./my-conversation.json