For various reasons, big Nix attrsets look ugly in the generated manual
page[1]. Use literalExample to fix it.
[1] Quotes around attribute names are lost, newlines inside multi-line
strings are shown as '\n' and attrs written on multiple lines are joined
into one.
- add missing types in module definitions
- add missing 'defaultText' in module definitions
- wrap example with 'literalExample' where necessary in module definitions