In spite of there being considerable documentation sometimes in the
config file, we go with CC0 because we don't want the notion of
'derived work' of a config file.
The example `settings.conf` is also CC0. Add some docs to
it while we're at it.
- a handful of modules had an unused *requires* key in module.desc;
this is probably from previous intentions around
prerequisites-testing. Since the settings were empty anyway,
they have been removed.
- [unpackfs] Compacted the way *requiredModules* list is written
- Remaining modules [networkcfg] [openrcdmcryptcfg] [rawfs] with
code that throws on bad configuration. Replace with meaningful
error messages, to better check cases of SyntaxError &c.
