Feature: Automatically output code in responses to files

[jschuur]

Ideas:

• any code snippet in the response gets saved to a file
• .gpt-output Subdirectory of local folder but default but support override
• handle file overwriting (date stamped or incrementing version number subdir?)
• detect file extension if response provides it in the markup
• one file per code snippet or all in one file? Pick one and have option to change default
• not on by default, but add .savecode command to do this from the REPL if not on
• specify default file extension to use (.savecode js)