Build: create macro for creating the release process script

Build: create macro for creating the release process script

Refactor the creation of the release process script, from
`release.template` into a `macrodef`.
Add a new target `releaseScript`, so that the release script can be
created after the `tagRelease` target was run.
This is helpful if the `tagRelease` target is run by a different,
earlier process than the actual release creation process.