Improve module structure

[GDYendell]

Move more modules into directories and define public APIs in __init__.py

These probably could be done in separate PRs, each one is an isolated improvement

• attributes/
  • attribute.py
  • attr_r.py
  • ...
• controllers/
  • base_controller.py
  • controller.py
  • controller_vector.py
• methods/
  • method.py
  • command.py
  • wrappers/.py
• datatypes/
  • datatype.py
  • int.py
  • ...