Citable version

Mostly packaging changes.

• improve README.md
• add CITATION.cff
• add github action to test releases

Now support cross-compiling

On MacOS or linux, you should be able to cross-compile and produce a windows version (assuming you have the mingw complier installed).

No new features, this release is just changes to the Makefile.

Latest release

This is the same as before, but now all the .c and .h files needed to compile the program are present.

v2.6.0

Fixes to make calculation for large spheres more robust. Tested up to sphere sizes of 10,000