Moved and completed time preprocessors list (PR 439 child 1)

[valeriupredoi]

Before you start, please read CONTRIBUTING.md.

Tasks

• Create an issue to discuss what you are going to do, if you haven't done so already (and add the link at the bottom)
• This pull request has a descriptive title that can be used in a changelog
• Add unit tests
• Public functions should have a numpy-style docstring so they appear properly in the API documentation. For all other functions a one line docstring is sufficient.
• If writing a new/modified preprocessor function, please update the documentation
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This alleviates some of the burden from PR #439 that will be now be broken into smaller bits - this is the first child

[valeriupredoi]

hey guys @bouweandela @schlunma @zklaus can I get a quick approval on this one so I can merge in master and go on producing #439 children pls? 🍺

[zklaus]

PS: It would have been helpful to have a sentence in the PR description on what this is trying to achieve. I was able to deduce it from the code only because it was so small and well-written.

[valeriupredoi]

cheers boss! 🍺

[valeriupredoi]

I will add plenty of info to the other ones, gimme a sec, merge this in the next now 🚜