Use flake8 instead of pyflakes and pep8

It combines both tools

Makefile

@@ -36,12 +36,11 @@ install: youtube-dl youtube-dl.1 youtube-dl.bash-completion youtube-dl.zsh youtu
 	install -m 644 youtube-dl.fish $(DESTDIR)$(SYSCONFDIR)/fish/completions/youtube-dl.fish
 
 codetest:
-	PYFLAKES_OUT=$$(pyflakes youtube_dl | grep -v youtube_dl/extractor/__init__.py); \
-	if test -n "$$PYFLAKES_OUT"; then \
-		echo "$$PYFLAKES_OUT"; \
+	FLAKE8_OUT=$$(flake8 --ignore E501 . | grep -v youtube_dl/extractor/__init__.py); \
+	if test -n "$$FLAKE8_OUT"; then \
+		echo "$$FLAKE8_OUT"; \
 		exit 1; \
 	fi
-	pep8 . --ignore E501
 
 test:
 	#nosetests --with-coverage --cover-package=youtube_dl --cover-html --verbose --processes 4 test