This allows the same function to be used with different commands.
Recent improvements to the parser stopped adding labels for bare words
"word" in the CLI schema, to reduce the chance of label conflicts, eg {
"get", "file", "<file>" }. Now a backslash-prepended word in the schema
"\word" will cause the matched argument to be labelled "word", just like
"[word]" does except "\word" is not optional.
Change a test case: configuration options are now case sensitive.
Fix config file load and parse logic in conf.c, always copy 'debug' flags
from config.debug.
The config schema 'interfaces' option is no longer MANDATORY.
Introduce new CLIFLAG_PERMISSIVE_CONFIG to supress bad-config ERROR messages
from the 'config set' and 'config get' commands.
Refactor cli_execute() into cli_parse() and cli_invoke(). Use *const* struct
command_line_option everywhere.
