add function to retrieve ziplist size in bytes

ziplist.c

@@ -411,6 +411,11 @@ unsigned int ziplistLen(unsigned char *zl) {
     return len;
 }
 
+/* Return size in bytes of ziplist. */
+unsigned int ziplistSize(unsigned char *zl) {
+    return ZIPLIST_BYTES(zl);
+}
+
 void ziplistRepr(unsigned char *zl) {
     unsigned char *p, encoding;
     unsigned int l, lsize;

ziplist.h

@@ -10,4 +10,5 @@ unsigned int ziplistGet(unsigned char *p, unsigned char **e, unsigned int *elen,
 unsigned char *ziplistDelete(unsigned char *zl, unsigned char **p);
 unsigned char *ziplistDeleteRange(unsigned char *zl, unsigned int index, unsigned int num);
 unsigned int ziplistCompare(unsigned char *p, unsigned char *entry, unsigned int elen);
-unsigned int ziplistLen(unsigned char *zl);
\ No newline at end of file
+unsigned int ziplistLen(unsigned char *zl);
+unsigned int ziplistSize(unsigned char *zl);