* Editor: Auto-save on a background goroutine so you don't randomly freeze
the editor up during.
* Fix actor linking issues when you drag and re-place a linked doodad: the
level was too eagerly calling PruneLinks() whenever a doodad was 'destroyed'
(such as the one just picked up) breaking half of the link connection.
* Chunk unloader: do not unload a chunk that has been modified (Set or Delete
called on), keep them in memory until the next ZIP file save to flush them
out to disk.
* Link Tool: if you clicked an actor and don't want to connect a link, click
the first actor again to de-select it.
Updates to the `doodad` tool:
* `doodad edit-level --resize <int>` can re-chunk a level to use a different
chunk size than the default 128. Large chunk sizes 512+ lead to performance
problems.
Noah Petherbridge
75fa0c7e56