Add tox for testing with different Python versions.

Makefile

@@ -14,7 +14,7 @@ docs:
 	pandoc -s -w markdown docs/header.md docs/install.md docs/body.md -o README.md
 
 lint:
-	@flake8 ./ --config=setup.cfg
+	@flake8 ./ --config=tox.ini
 
 release: docs
 	# Check for tag existence
@@ -38,6 +38,6 @@ tar:
 	git archive --format=tar --prefix autojump_v$(VERSION)/ $(TAGNAME) | gzip > autojump_v$(VERSION).tar.gz
 	sha1sum autojump_v$(VERSION).tar.gz
 
-test:
+test: lint
 	@find . -type f -iname "*.pyc" -delete
-	py.test -rsxX -q
+	tox