Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
Use std::unique_ptr to guard against leaking the new'd pointers
in SEXPR lists if there is an exception during parse.
This was noticable during the Sexpr/ParseExceptions unit test.
Fixes: lp:1830209
* https://bugs.launchpad.net/kicad/+bug/1830209
The SEXPR class is a useful general-purpose S-Expression library
class and can (maybe) be used else where. It also should get
test coverage, as even if noone else uses it, it's critical for the
kicad2step exporter.
Also add some test coverage for some kicad2step routines. For now,
they're not useful outside kicad2step, but they are at least a useful
reference for S-Expression parsing.
