3.1.1

Many commits, few changes

• dependency updates
  • added ext-gd to composer.json as it is required for the default settings
  • PHPUnit 8.3
  • added PHP 7.4 snapshot to .travis.yml
• cleanup:
  • QRImage::$background removed as it was unnecessary (now local in QRImage::dump())
  • use function imports
  • sprintf() for several messages and other output
  • format of QRMatrix::formatPattern and QRMatrix::versionPattern changed from hex to binary for better comprehensibility
  • QROptionsTrait::__set() removed in favor of SettingsContainerInterface setters set_versionMin(int $version) and set_versionMax(int $version)
  • additional coverage tests