Don't ignore existing store options when applying NSReadOnlyPersistentStoreOption
Thanks to Richard Buckle for pointing this out! https://github.com/karelia/BSManagedDocument/pull/8/files#L1R123
typo
Avoid what could maybe maybe be a tiny race condition since async saving was introduced
Make a bunch of small tweaks and comments as suggested by Richard Buckle's review
https://github.com/karelia/BSManagedDocument/pull/8/files