Add tox

- Put extras_require to setup.py
- Add mypy

mypy.ini

@@ -0,0 +1,12 @@
+[mypy]
+warn_unused_ignores = True
+ignore_missing_imports = True
+strict_optional = False
+check_untyped_defs = True
+disallow_incomplete_defs = True
+disallow_untyped_defs = True
+disallow_any_generics = True
+disallow_untyped_calls = True
+warn_redundant_casts = True
+warn_unused_configs = True
+strict_equality = True