Introduced the Build ID in INFO and --version output.

The idea is to be able to identify a build in a unique way, so for
instance after a bug report we can recognize that the build is the one
of a popular Linux distribution and perform the debugging in the same
environment.

src/crc64.h

@@ -0,0 +1,8 @@
+#ifndef CRC64_H
+#define CRC64_H
+
+#include <stdint.h>
+
+uint64_t crc64(uint64_t crc, const unsigned char *s, uint64_t l);
+
+#endif