Calculate minimum distance between two GeoFeatures

[EwoutH]

Adds a minimum-distance-of function to the NetLogo GIS Extension.

This combines #17, #18 and #19, originally written by @josephzhao.

[LaCuneta]

Hey, thanks for pulling this together. Unfortunately when I went to compile it I found a bunch of syntax errors in the code. As such I suspect this may not actually work as I don't think the author could've actually tested it, but I may be wrong. I left comments on the code issues.

Other things I'd want to see before merging:

• Add at least one, and maybe more, language tests for this functionality. You can read about language tests in the NetLogo wiki, and there are a lot of examples already in the GIS test file. You can run the tests with sbt test
• We'd need the prim added to the documentation. The short version is to edit documentation.conf then run sbt extensionDocument to generate the README.md and commit both files. You can check out the netlogo-extension-documentation plugin for more info.

If you get things working just let me know and I'll be happy to re-test and merge.

[EwoutH]

Thanks a lot for the quick and extensive reply. I fixed the cases you mentioned in the review in 34a1ecb.

Unfortunately, I'm not a Java dev (and to be honest, not thinking of becoming one), so further development and testing is difficult for me. So this is probably as far as I can get this PR. Maybe @josephzhao is still interested in finishing what he started, or you or someone else want to finish it.

I've checked the "Allow edits by maintainers" checkbox on this PR. I also think you can go to https://github.dev/NetLogo/GIS-Extension/pull/46 (notice the .dev) and add commits to this PR. And otherwise, (anyone) feel fully free to take the patch of this PR and build on from there.