todo

- flag to drop prefix in shellvars mode (strip selector, string, num elements)
- filter out an item (exclude a subtree)
- compile configs (annotated with source)
- comment processing
- error messages with line # (libucl)
- variable in rc.conf to rewrite configs to libucl
- global config file, includes other configs in a namespace (show running config)
- (search for *.ucl)
- permission warnings, verbose option
- 
- for utils like sshd, ucl -> old config utilities

- (libucl) include command force a prefix (namespace)
- include an entire file as a value (motd)
- etc/defaults ucl.rules (motd)



.disable
.delete
.merge=error|replace|merge|append


shell mode replace . with _ in __keys
support single quotes
bools as ints
escaping (\ " etc) steal code from pkgconf getline.c
arrays-as-objects mode

shell library to do the shell interpretation of --shellvars mode

prefix all keys with a _something_