Merge branch 'jt/decorate-api'

A few structures and variables that are implementation details of
the decorate API have been renamed and then the API got documented
better.

* jt/decorate-api:
  decorate: clean up and document API

builtin/fast-export.c

@@ -895,7 +895,7 @@ static void export_marks(char *file)
 {
 	unsigned int i;
 	uint32_t mark;
-	struct object_decoration *deco = idnums.hash;
+	struct decoration_entry *deco = idnums.entries;
 	FILE *f;
 	int e = 0;