don't run purenix for corefn.json files that are older than the output default.nix file #25
Description
Right now, when you run purenix, it looks for all the output/*/corefn.json files, and transpiles each of them to output/*/default.nix.
It may be possible to instead check if an output/*/default.nix file is newer than output/*/corefn.json, and not regenerate the output/*/default.nix in that case.
We should confirm that purs has similar functionality, and doesn't touch the corefn.json file when it is already newer than the input src/*.purs input file.
There was a little discussion about this in #22 (comment).