With `builtins.functionArgs` we can get some information if the first argument
is an attrset and whether the contained fields have default values. Encode that
into the pretty-printed lambda.
They both reference the toJSON builtin, so we get semantic identifiers
that express the intent of the generation.
Both should be able to map each nix value (minus functions) to the
destination config files.
Includes two invocation unit tests.
Many configurations are INI-style files. Attribute sets can be mapped
rather painlessly to the INI format.
This adds a function toINI inside a new generators library section.
Also, unit tests for the default values are provided.
