Rename *.ql files to *.overpassql

[FloEdelmann]

*.overpassql is now the recommended file extension for Overpass QL: OSM Wiki: Overpass QL § File extension
(Disclaimer: I added that section after some discussion.)

I propose to rename all *.ql files in this repo to *.overpassql for consistency.

Context: GitHub's syntax highlighting engine requires that 200 repositories use the same file extension before they consider supporting that syntax and file extension: github-linguist/linguist#5890

[FloEdelmann]

Thanks for renaming!

[praszuk]

Thank you for your effort to standardize it. I just want to add, that you probably missed some repos that contain overpass files, but with .txt extension like this one (same organization) 😄

[FloEdelmann]

Feel free to rename it there, too, of course 😉
It's difficult to find all files of course; another benefit of the standardized file extension 🙂