Publish the k0s_sort binary

[kke]

Adds a couple of features to the k0s_sort binary and publishes it as release assets.

Usage: k0s_sort [options] [filename ...]
  -l	only print the latest version from input
  -o	print the latest version from online
  -s	omit prerelease versions
  -v	print k0s_sort version

[twz123]

Any reason for the rename? I think it makes sense to have a main.go that contains the main function. I'm always a bit hesitant to use underscores in go file names, as this is also a mechanism used for conditional compilation.