Allow folders to not be sorted before files

[npezza93]

Is your feature request related to a problem? Please describe.
No problem

Describe the solution you'd like
I'd like a configuration option to not group folders before files and instead have them all listed alphabetactically.

What it currently looks like

Describe alternatives you've considered
N/A

Additional context
I didnt see a config option but let me know if imissed it!

[alex-courtis]

sort_by provides several sorting options however a directory option would not be appropriate, as it is orthogonal to the existing options.

An additional option like sort_directories_first would be appropriate.

PRs are very welcome.