[[feature-stackdir]] Create object directories.
[[feature-stackdir]] Stub in most remaining object save functions.
[[feature-stackdir]] Add helper function for writing UTF-8 files.
[[feature-stackdir]] Refine MCStackdirIOSaveVersion().

* Add error information if saving fails.
* Use MCStackdirIOSaveUTF8().
[[feature-stackdir]] Add name and string formatting.
[[feature-stackdir]] Save object "_parent" and "_kind" files.