Bugfixes and cleanups

[amrox]

Thank you for sharing this script! I had to edit it a bit so it worked with my note export. I hope you find the changes useful.

[philgyford]

Thanks for this. I should have thought about moving the sanitisation before the check for duplicates!

I've always preferred being explicit about boolean comparisons, so if foo is True: rather than just if foo: but I see PEP8 seems to prefer the latter so fair enough!