Makefile: break each check into own rule.

Makefile

@@ -10,10 +10,14 @@ OUTPUT_FLAGS = --path-base /code/muppet-strings/output \
 output:
 	python -m muppet  $(OUTPUT_FLAGS)
 
-check:
+check_style:
 	flake8 muppet
+
+check_type:
 	mypy -p muppet
 
+check: check_style check_type
+
 # TODO only require coverage if `python -m pytest -VV | grep pytest-cov` return true
 PYTEST_FLAGS = --cov=muppet --cov-branch --cov-report=html