By making the caller use the "namespace" keyword, the formatter
is given the right indentation hints.
Also makes it clearer synatactically. One day, this will be a
namespace alias (needs GCC 7).
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.
John Beard