This patch rebuilds DiaryEntryIterator to be a wrapper around
StoreIdIterator and thus `Diary::entries()` to use `Store::entries` and
not `Store::retrieve_for_module()`.
The `Store::retrieve_for_module()` function is somehow buggy and loads
contents of the files into memory and _somehow_ causes the entries to be
rewritten without newlines.
This bug is fixed by moving away from `Store::retrieve_for_module()`.
This patch removes unused crate imports reported by newer rust versions.
Some crates were only required for tests, some only for tests with
macro_import - these things were fixed with feature gates.
