Improve pypesa directory structure

[SentinelWarren]

Greetings @Kalebu , so this just a suggestion on the package structure improvement. Suggestion list goes as follows;

• Use __init__.py to only Import key classes | methods from modules directly into the package namespace. i.e the folder structure could then be;

  pypesa/
  __init__.py
  mpesa.py
  mpesa_execptions.py
  service_urls.py

• __init__.py could also include other important parameters like, version, author, release date, doc-string with a decent sample usage etc etc.
• Add a tests folder with the following structure;

  tests/
  __init__.py
  test_pypesa.py

  Note, tests/__init__.py can/should be left empty.

• Any other structural improvements that i haven't listed/noticed yet.

So to sum up, i think i can working on this if you think it might be a good idea. Also, i think there other code related improvements suggestion(mostly on the OOD), that i will definitely create their own separate issues.

[Kalebu]

Hi Warren

Thanks for taking your time putting all together

I think its great idea, you can proceed with the changes

• update the documentation for every change you make

Let me incase of anything

Best regards Kalebu