split into submodules

the Config module was getting very long and hard to reason about.
fix eval mode

any attempt at using eval mode was resulting in the following error:

  Won't typecheck:
          No instance for (Data.String.IsString GHC.Types.Bool)
    arising from the literal `"False"'
  Possible fix:
    add an instance declaration for
    (Data.String.IsString GHC.Types.Bool)