Readme: Use filenames from source

Instead of using filenames in the release package, use filenames from the source package. The filenames will be translated with the `make_package` script.
make_package: Rename filenames in readme and cleanup

* Source-package filenames in the readme file are now translated to release-package filenames.
* Cleaned up readme file processing.
* Allowed to run the script from Windows with warning messages.