Adding object table (#1)

* code for maintaining the object table

* Makefile fix

* Clone git submodules.

* directory -> object_table

* Fix Makefile and remove unnecessary files.

* Fix formatting.

* make code more generic

common.h

@@ -0,0 +1,29 @@
+#ifndef COMMON_H
+#define COMMON_H
+
+#include <errno.h>
+
+#ifdef NDEBUG
+#define LOG_DEBUG(M, ...)
+#else
+#define LOG_DEBUG(M, ...) \
+  fprintf(stderr, "[DEBUG] (%s:%d) " M "\n", __FILE__, __LINE__, ##__VA_ARGS__)
+#endif
+
+#define LOG_ERR(M, ...)                                                     \
+  fprintf(stderr, "[ERROR] (%s:%d: errno: %s) " M "\n", __FILE__, __LINE__, \
+          errno == 0 ? "None" : strerror(errno), ##__VA_ARGS__)
+
+#define LOG_INFO(M, ...) \
+  fprintf(stderr, "[INFO] (%s:%d) " M "\n", __FILE__, __LINE__, ##__VA_ARGS__)
+
+#define UNIQUE_ID_SIZE 20
+
+typedef struct { unsigned char id[UNIQUE_ID_SIZE]; } unique_id;
+
+/* Convert a 20 byte sha1 hash to a hexdecimal string. This function assumes
+ * that buffer points to an already allocated char array of size 2 *
+ * UNIQUE_ID_SIZE + 1 */
+char *sha1_to_hex(const unsigned char *sha1, char *buffer);
+
+#endif