Make version depend on git tag

Makefile

 TARGET=md5toc
-MD5TOC_VERSION=20160721
+MD5TOC_VERSION=$(shell git describe | sed -e 's/^v//')
 SOURCES=Makefile md5toc.c md5toc.spec config.h md5.c md5.h
 CFLAGS=-Wall -Werror -I. -DMD5TOC_VERSION='"$(MD5TOC_VERSION)"'