object_type: mark old values as deprecated

Mark old object type values as `static const` so that we can mark them
as deprecated with the `GIT_DEPRECATED` macro.

Author: ethomson

include/git2/types.h

@@ -450,16 +450,16 @@ typedef struct git_mailmap git_mailmap;
 
 /**@{*/
 
-#define GIT_OBJ_ANY        GIT_OBJECT_ANY
-#define GIT_OBJ_BAD        GIT_OBJECT_BAD
-#define GIT_OBJ__EXT1      0
-#define GIT_OBJ_COMMIT     GIT_OBJECT_COMMIT
-#define GIT_OBJ_TREE       GIT_OBJECT_TREE
-#define GIT_OBJ_BLOB       GIT_OBJECT_BLOB
-#define GIT_OBJ_TAG        GIT_OBJECT_TAG
-#define GIT_OBJ__EXT2      5
-#define GIT_OBJ_OFS_DELTA  GIT_OBJECT_OFS_DELTA
-#define GIT_OBJ_REF_DELTA  GIT_OBJECT_REF_DELTA
+GIT_DEPRECATED(static const int) GIT_OBJ_ANY = GIT_OBJECT_ANY;
+GIT_DEPRECATED(static const int) GIT_OBJ_BAD = GIT_OBJECT_BAD;
+GIT_DEPRECATED(static const int) GIT_OBJ__EXT1 = 0;
+GIT_DEPRECATED(static const int) GIT_OBJ_COMMIT = GIT_OBJECT_COMMIT;
+GIT_DEPRECATED(static const int) GIT_OBJ_TREE = GIT_OBJECT_TREE;
+GIT_DEPRECATED(static const int) GIT_OBJ_BLOB = GIT_OBJECT_BLOB;
+GIT_DEPRECATED(static const int) GIT_OBJ_TAG = GIT_OBJECT_TAG;
+GIT_DEPRECATED(static const int) GIT_OBJ__EXT2 = 5;
+GIT_DEPRECATED(static const int) GIT_OBJ_OFS_DELTA = GIT_OBJECT_OFS_DELTA;
+GIT_DEPRECATED(static const int) GIT_OBJ_REF_DELTA = GIT_OBJECT_REF_DELTA;
 
 #define git_otype git_object_t