Retrieves a comment above key from group_name.
If key is null then comment will be read from above group_name.
If both key and group_name are null, then comment will be read
from above the first group in the file.
Note that the returned string does not include the '#' comment markers, but does include any whitespace after them (on each line). It includes the line breaks between lines, but does not include the final line break.
| this |
a KeyFile |
| group_name |
a group name, or null |
| key |
a key |
|
a comment that should be freed with g_free |