Refactoring generation of kanwa dict

Added

• Add type hinting.

Changed

• Refactoring dictionary generation classes.
• call super() from wakati.init()
• test: detection whether tox or raw pytest by TOX_ENV environment variable.
  When raw pytest, generate dictionaries as fixture.
  Previous versions uses --runenv option for pytest.

Fixed

• NewAPI: fix return value when empty input string.