conf.c: fix indentation

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
conf.c: separate out INI parsing code

Introduce a generic callback-based INI parser.  This has the side-effect
of making errors in included files fatal as the callback does not know
if it is in the main file or an Include.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>