refactor: Use pathlib for paths

[moritzscholz]

Hey!

Are you accepting contributions for this?

Is this going in the right direction? I thought it'd be good to first change the internal path-handling to use pathlib and then deal with passing the paths around as pathlib.Path objects instead of strings.

Resolves #23 .

[moritzscholz]

I also slightly refactored hb_editor.WriteToTemp and noticed something. You write:

# snip
                if not os.path.exists(Settings.editor_temp_root):
                    os.mkdir(Settings.editor_temp_root)
# snap

But shouldn't it be Settings.getInstance().editor_temp_root?