Ben Prather

> My only comment right now is to please add a cmake compile time option to use the old parser without any modifications. Downstream codes should be able to opt...

> After some time to digest parts of this, it looks like it's backwards compatible with the input file format (which was my main concern), so as long as this...

@par-hermes format This now passes all tests except the hdf5 output format (as expected -- parameters are now dumped to outputs/restarts in TOML) and the `CheckDesired`/`CheckRequired` unit test (now commented...

I've rebased this on top of @Yurlungur's #1283, which in the process considerably simplified aspects of that PR, and I think I could cut it down the line count further...