Type cleanup, internally and in the API.  Fixes most llvm warnings.
diff --git a/lib/zip_set_archive_comment.c b/lib/zip_set_archive_comment.c
index bf72983..297798a 100644
--- a/lib/zip_set_archive_comment.c
+++ b/lib/zip_set_archive_comment.c
@@ -40,7 +40,7 @@
 
 
 ZIP_EXTERN int
-zip_set_archive_comment(struct zip *za, const char *comment, int len)
+zip_set_archive_comment(struct zip *za, const char *comment, zip_uint16_t len)
 {
     struct zip_string *cstr;