Update to version 0.18.0

ChangeLog:

• Dropped Python 2 and Python 3.5
• Using pathlib.Path() as an output instead of str in most places:
  • Project.path
  • Script.path
  • Definition.module_path
  • Refactoring.get_renames
  • Refactoring.get_changed_files
• Functions with @property now return property instead of function in Name().type
• Started using annotations
• Better support for the walrus operator
• Project attributes are now read accessible
• Removed all deprecations