to suppress warnings about `errtxtf` operand number "%<n>$" args;
enable some further warnings
test suite: enable -Wpedantic and fix/suppress any warnings
allow for old "libpng" (`png_set_scale_16()` not available)
general: Solaris compat
library: use proper function ptr instead of `void *` for function
table; warning suppression "-Wpedantic" -> "-Wstrict-prototypes"
GRIDMATRIX/HANXIN/QRCODE: `xx_define_mode()`: multi-dim `char_modes`
outputting to in-memory buffer `symbol->memfile` instead of to
file `symbol->outfile`, ticket #301
Add "README.clang-tidy" and ".clang-tidy" options file
Suppress some warnings
