We do this by adding to included_files as i3 processes the configs.
This should allow for easy debugging, without having to change how i3 processes
config files.
related to #4192
The implementation uses wordexp(3) just like sway:
https://github.com/i3/i3/issues/1197#issuecomment-226844106
Thanks to jajm for their implementation at
bb55709d0a
This required refactoring the config parser to be re-entrant
(no more global state) and to return an error instead of dying.
In case a file cannot be opened, i3 reports an error but proceeds with the
remaining configuration.
Key bindings can be overwritten or removed using the new --remove flag of the
bindsym/bindcode directive.
All files that were successfully included are displayed in i3 --moreversion.
One caveat is i3 config file variable expansion, see the note in the userguide.
fixes#4192
