[enh] #54 add black as dev dependency and in MakeFile (check and black commands)

Makefile

-.PHONY: docs tests check mypy pylint
+.PHONY: docs tests check mypy pylint black
 
 # generate documentation
 docs:
@@ -9,7 +9,7 @@ tests:
 	python3 -m unittest ${TESTS_FILTER}
 
 # check
-check: mypy pylint
+check: mypy pylint black
 
 # check static typing
 mypy:
@@ -18,3 +18,7 @@ mypy:
 # check code errors
 pylint:
 	pylint --disable=C,R0913,R0903,R0902,R0914,R0912,R0915,W0613 --enable=C0121,C0202,C0321 --jobs=0 duniterpy/
+
+# format code
+black:
+	black duniterpy

requirements_dev.txt

 coveralls
 mypy
 pylint
+black
 sphinx
 sphinx_rtd_theme