XRechnung Visualization 2021-11-15 compatible with XRechnung 2.1.1

Added

• Added documentation about architecture and usage
• Added support for localization -- English and German output is supported. This was done for HTML and PDF output.
• Added BT-26 to maxRechnung.xml

Changed

• Enhanced accessibility of HTML output
• PDF output is now accessible (PDF/UA level), fonts are embedded into PDF (thx to @kosek)
• Saxon version is configurable with properties (thanks to GitHub user @knoxyz)
• Default saxon version is set to HE-10.6
• Rewrote README.md for more details and added links to documentation

Fixed

• Fixed format-date of BT-26 in xrechnung-html.xsl (thanks to GitHub user @knoxyz)
• BT-30-Scheme-ID visualized