support memory for functions

[Fei-Wang]

Before submitting

Add memory support for OpenAIFunctionsAgent like StructuredChatAgent.

Who can review?

@hwchase17

[Fei-Wang]

@hwchase17
Hello, memory is very useful in application scenarios. For example, there is a function to calculate bmi, the height and weight are provided for the first time, and gpt returns the calculation result. For the second time, it can be said that if the weight is xxx, gpt will calculate bmi based on memory.

However, I noticed that the files for the master branch have changed, and I can handle conflicts if necessary.

[vercel]

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