dg1d: allow parameter overriding on cmd line
Allows to use main(parfile, "Mesh.n" => "1") to override the value given in the parfile.
To do this we
- parse the TOML file
- flatten the dict-of-dicts to a single dict with the keys joined by a
. - insert the parameters
- unflatten the dict to a dict-of-dicts
- write this to the output directory
Unfortunately, TOML.jl does not allow to parse into OrderedDict.
This causes the newly written parfiles to be messed up.
Furthermore, by manually re-writing the parfiles we also do not preserve any comments or formatting.