Minor refactor, dependency clarification, doc blocks, and whitespace

- Extracts scattered instances of `\Class` to `use Class;`
- Consolidates `find()`
- Adds possible TODOs via `@todo`
- Removes `Str` facade in favor of `str_random()` helper method
- Clarifies what is being returned from functions
    - `delete()` was not returning anything
    - Clarifies reason for assumed success on `deleteNotesOlderThan()`
- Minor whitespace/alignment