Use git export-subst for versioning when not in git repo.

dopey · dopey · commit ecc1c7b0d669 · 2019-02-19T13:11:08.000-08:00
Add .VERSION file that is automatically populated by `git archive`
setting version info when not in an active git repository. Useful when
downloading a tarball.
diff --git a/.VERSION b/.VERSION
@@ -0,0 +1 @@
+$Format%d$
diff --git a/.gitattributes b/.gitattributes
@@ -0,0 +1 @@
+.VERSION export-subst
