0.4.0

New

• add max_flatten_depth to flatten() (#22, #31, #35)

Change

• made pathlib2 optional for Python < 3.4 (#32)
• use poetry-core instead of poetry in pyproject.toml (#36)
• deprecate flatten_dict.splitter in favor of flatten_dict.splitters (#38)
• deprecate flatten_dict.reducer in favor of flatten_dict.reducers (#38)

Code Quality

• improve code quality (#32)
• test for Python 3.9 (#34)