mkinvoice will generate a PDF invoice from a YAML-file

It is the by-result of learning the Golang language, but with the
purpose to generate PDF-Invoices for nbit Informatik GmbH

Font File can be generated with makefont

To generate the QRCode, following library is used:
https://github.com/stapelberg/qrbill

Usage (Example):
$ ./mkinvoice yaml/123456.yml

Joerg Lehmann, December 2020