Add version info from git-describe

A new script, gen-version.sh, is now invoked from 'make version' to generate
the file VERSION. This file contains a version identifier generated by
git-describe and is included in the Makefile.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

gen-version.sh

@@ -0,0 +1,4 @@
+v=$(git-describe --abbrev=4 HEAD | sed -e 's/-/./g')
+test -z "$v" && exit 1
+echo "CGIT_VERSION = $v"
+echo "CGIT_VERSION = $v" > VERSION