added a pylint tester

Makefile

+.PHONY: test
+test:
+	# Testing the python files via pylint3.
+	@for FILE in *.py; do \
+		REPORT="$$(pylint3 --disable=invalid-name,missing-docstring "$$FILE" 2>&1)"; \
+		if ! [ $$? = 0 ]; then \
+			printf '%s\nThe above report is for file "%s".\n' "$$REPORT" "$$FILE"; \
+			exit 1; \
+		fi; \
+	done; \
+	printf 'All OK.\n'