Add new build targets & update workflows

[callsop]

workflows:

• updated release workflow to match the same steps of the build workflow
• moved each platform to the makefile (unixpackage & winpackage)

makefile:

• ensure 'clean' cleans both packages always
• added 'allpackages' target to build all the packages in one go

[tlindner]

Is it going to be an issue we're making tar archives for windows? And not zip?

[callsop]

Not for me 😂
Seriously though, maybe best to change it. I'll update this PR shortly.

[callsop]

• updated to use zip for windows package
  cc: @tlindner

[tlindner]

Oh no, the release didn't include any executables!