nlohmann has customization points for exception throws. we can use these
instead and wrap json exceptions at the source instead of playing a game
of whack-a-mole with json errors all over the tree. since nlohmann needs
macros set to achieve this we can no longer precompile its headers *and*
must forbid including it anywhere without the proper defines or ordering
of include directives will break lix with ODR violations, if we see them
at all before we get another json-related bug report. a new lint will be
in charge of ensuring this doesn't happen. we also re-allow direct calls
to nlohmann json parsing since error handling is no longer a problem. we
will keep the wrapper for more convenient error context handling though.
fixes#1092
Change-Id: I54ecc14f5bec5e2177729b41c3703216e76cc6a3
eldritch horrors
56d6ac3114