Upgrade Guides

The following chapter provides guides to upgrade from one major version to the next major version. This includes only breaking changes, for a complete changelog please see https://github.com/bithost-gmbh/pdfviewhelpers/blob/master/CHANGELOG.md . If there is something missing in one of these guides please tell us via mail, a GitHub issue or even better a pull request!

• Upgrading from 1.x.x to 2.x.x