Restraining a Picture in one dimension with a Frame should make it
report the right overall dimensions (keeping its aspect ratio).
Also applying the F.9 C++ Core Guideline.
Publishing my old invoice layouter in a reusable scripting-based form,
rather than an annoyingly fixed binary.
Because Lua compiled for C++ might be hard to find, we provide a wrap.
Curiously, only GitHub releases seem to contain onelua.c,
which is a very handy file.
We could have also subprojected libqr, which is in the public domain,
however the other main dependencies are also LGPL like libqrencode is.
And it is likely to be installed.
The user manual also serves as a test.
