Creates a keyfile-backed GSettingsBackend.
The filename of the keyfile to use is given by filename.
All settings read to or written from the backend must fall under the
path given in root_path (which must start and end with a slash and
not contain two consecutive slashes). root_path may be "/".
If root_group is non-NULL then it specifies the name of the keyfile
group used for keys that are written directly below root_path. For
example, if root_path is "/apps/example/" and root_group is
"toplevel", then settings the key "/apps/example/enabled" to a value
Creates a keyfile-backed GSettingsBackend. The filename of the keyfile to use is given by filename. All settings read to or written from the backend must fall under the path given in root_path (which must start and end with a slash and not contain two consecutive slashes). root_path may be "/". If root_group is non-NULL then it specifies the name of the keyfile group used for keys that are written directly below root_path. For example, if root_path is "/apps/example/" and root_group is "toplevel", then settings the key "/apps/example/enabled" to a value