This PR adds an example of doing question answering over documents using
OpenAI Function Agents.
#### Who can review?
@hwchase17
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Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>
#### Before submitting
Add memory support for `OpenAIFunctionsAgent` like
`StructuredChatAgent`.
#### Who can review?
@hwchase17
---------
Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>