Version 3 of the plugin is a complete rewrite and a lot has been simplified.
In previous versions, the dependency on Contao was specified as contao/core. In version 3, the requirements
should be specified to be compatible with Contao 4. The basic dependency should be contao/core-bundle. If
you need news, you must also add contao/news-bundle and so on.
Be aware that you can still be compatible with Contao 3. If your extension supports Contao 3.5 and Contao 4,
simply add a requirement for contao/core-bundle: >=3.5,<5.
In previous versions of the plugin, it was possible not to specify any sources. The plugin then tried to
guess how your plugin looks like, and simply link all files into a package name ("vendor/name") folder
in system/modules. This is no longer supported, you must specify your sources or nothing will be installed.
Older versions of the plugin supported file maps for shadow-copies and symlinks instead of just sources.
This was meant to allow the developer to decide the mode of installation. Support for this has been dropped in
version 3, the plugin will decide how to install the files.