Add Ceres version and ABI version defines to ceres.h

This will make it possible to write code which detects Ceres
versions and does different things with different versions.
Ideally this wouldn't be necessary, but in practice it is
sometimes useful.

Change-Id: I8d9f56d664ef75706e87c9bd7954e709dd7c0278

include/ceres/ceres.h

diff --git a/include/ceres/ceres.h b/include/ceres/ceres.h
index 22aaf8f..2db19cb 100644
--- a/include/ceres/ceres.h
+++ b/include/ceres/ceres.h
@@ -34,6 +34,9 @@
 #ifndef CERES_PUBLIC_CERES_H_
 #define CERES_PUBLIC_CERES_H_
 
+#define CERES_VERSION 1.3.0
+#define CERES_ABI_VERSION 1.3.0
+
 #include "ceres/autodiff_cost_function.h"
 #include "ceres/cost_function.h"
 #include "ceres/iteration_callback.h"