Improved the composer package definition

- changed the autoload from files to classmap to really use autoloading (files is not autoloading, it is eagerloading needed for files defining functions rather than classes)
- removed the explicit version in the file, as this causes more harm than good for packages stored in VCS repos: Composer ignores it for branches, and will consider tags as invalid if the explicit version does not match the version generated based on the tag name.