Package distribution

[mreso]

What does this PR do?

This PR prepared the repo in a way that llama-recipes can be distributed as a package for easier usage and development.
For this the following changes are made:

• Move source files int src/llama_recipes
• Add pyproject.toml for building wheel
• Make script runnable with python -m
• Adopt documentation
• Adding basic unit tests

Fixes # (issue)
-NA-

Before submitting

• Did you read the contributor guideline,
  Pull Request section?
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Thanks for contributing 🎉!

[chauhang]

@mreso Thanks for getting packaging sol started. Great to see pip install option and unit tests added. Please look into adding a contributors readme as well for developers with a section on unit tests and how to add new tests.

The main inference example does not seem to generating the summary correctly. Please check if anything has changed there.

Left few other comments inline.