added one-step realese script 'make release version=nn' - closes #158

Makefile

@@ -37,4 +37,14 @@ install:
 	install -m 644 --owner root --group root youtube-dl.1 /usr/local/man/man1
 	install -m 644 --owner root --group root youtube-dl.bash-completion /etc/bash_completion.d/youtube-dl
 
-.PHONY: all update-latest readme man-page bash-completion compile exe install
+release:
+	@if [ -z "$$version" ]; then echo 'ERROR: specify version number like this: make release version=1994.09.06'; exit 1; fi
+	@if [ ! -z "`git tag | grep "$$version"`" ]; then echo 'ERROR: version already present'; exit 1; fi
+	@if [ ! -z "`git status --porcelain`" ]; then echo 'ERROR: the working directory is not clean; commit or stash changes'; exit 1; fi
+	@sed -i "s/__version__ = '.*'/__version__ = '$$version'/" youtube_dl/__init__.py
+	make all
+	git add -A
+	git commit -m "release $$version"
+	git tag -m "Release $$version" "$$version"
+
+.PHONY: all update-latest readme man-page bash-completion compile exe install release