made it possible to pass additional tools to CodeInterpreterSession

[Valian]

This PR includes:

• a small change to session, making it accept arbitrary tools
• an example how these tools could be used

It's useful for me and I think it might be useful for others, hopefully you'll decide to include that feature.

Closes #18

[shroominic]

I think its recommended to use StructuredTools for the OpenAIFunctionsAgent because it needs some kind of functions schema and a StructuredTool forces this schema to be available.
Without this schema I encountered a lot of bugs and decreased performance because the current implementation to get around not having schemas is really hacky.
Maybe you can look into this part again and do some changes or convince me why your solution is right :)

[Valian]

StructuredTool is a Tool as well, but almost all lang-chain provided tools are not structured tools (yet). So making it a Tool allows to use these provided tools, even if it occasionally causes bugs with a function agent. We don't lose anything, but we gain ability to use some of these tools.

Another possible choice is to do not use function agent. It shines when functions have multiple parameters, but for code interpreter it's not the case.

[shroominic]

Okay nice lgtm :)