This reverts commit cad8957eabcbf73062226d28366fd446c15c8737. It
breaks NixOps, but more importantly, such major changes to the module
system really need to be reviewed.
- Enforce that an option declaration has a "defaultText" if and only if the
type of the option derives from "package", "packageSet" or "nixpkgsConfig"
and if a "default" attribute is defined.
- Enforce that the value of the "example" attribute is wrapped with "literalExample"
if the type of the option derives from "package", "packageSet" or "nixpkgsConfig".
- Warn if a "defaultText" is defined in an option declaration if the type of
the option does not derive from "package", "packageSet" or "nixpkgsConfig".
- Warn if no "type" is defined in an option declaration.
- add missing types in module definitions
- add missing 'defaultText' in module definitions
- wrap example with 'literalExample' where necessary in module definitions
