20220112

Switch to SO-5.7.3, so5extra-1.5.0, fmtlib-8.1.1.

Fixes for some warnings in C++20 mode.

20200128

Port to C++17, SO-5.7.0, so5extra-1.4.0 and fmtlib-6.1.2.

20190129

Actual version fixed as tag