API für AB 3.80 01/04

What's Changed

• added common-schema.xsd for e-invoicing by @aronkankel in #112
• Übernahme der Inhalte aus TechInfo-PDF in README by @aronkankel in #119
• English language support for README.md by @aronkankel in #122
• Adding badges for languages to README by @aronkankel in #123
• Adding language badges to README titles by @aronkankel in #124
• Changes for AB 3.80 01/04 by @aronkankel in #126

Full Changelog: 3.80.0100...3.80.0104