Makefile: added 'release' target.

Makefile

 RESOURCEDIR=$(PREFIX)/share/gitstats
 RESOURCES=gitstats.css sortable.js *.gif
 BINARIES=gitstats
+VERSION=$(shell git rev-parse --short HEAD)
 
 all: help
 
 	@echo "Usage:"
 	@echo
 	@echo "make install                   # install to /usr"
-	@echo "make install PREFIX=~     # install to ~"
+	@echo "make install PREFIX=~          # install to ~"
+	@echo "make release [VERSION=foo]     # make a release tarball"
 	@echo
 
 install:
 	install -v $(BINARIES) $(BINDIR)
 	install -v -m 644 $(RESOURCES) $(RESOURCEDIR)
 
-.PHONY: all help install
+release:
+	@tar --owner=0 --group=0 --transform 's!^!gitstats/!' -zcf gitstats-$(VERSION).tar.gz $(BINARIES) $(RESOURCES) doc/ Makefile
+
+.PHONY: all help install release