Move cache path into DocumentCache.
Move generating cache filenames into DocumentCache.
Move mapping cache filenames into DocumentCache.
Move removing files from cache into DocumentCache.
Share code for closing documents.
Move writing cache file into DocumentCache.
Move writable check into DocumentCache.
Move crashed check into DocumentCache.
Don't delete cache files when restoring from cache.
Don't delete cache files when closing program.
Backup cache on successful exit.
Always write to new cache files.
FIXED: Smart quotes were incorrect after opening punctuation.