Mark old nearest-point-on-line properties as deprecated

[EmilJunker]

This PR is a follow-up to #2867. I have found a way to properly mark the old nearestPointOnLine properties as deprecated without messing up the generated Readme docs. I modified the generate-readmes script slightly to make it work.

The result is what can be seen in #2867 (comment)

I also used this opportunity to switch the lineOverlap, lineSlice, lineSplit and pointToLineDistance functions over to the new properties. It would be a bit embarrassing if turf's own functions would continue to use properties marked as deprecated. 😉

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