From this version, xplr won't annoy the users to visit the upgrade guide
when there is no need.
Also, users will only get upgrade related notification when it is
there is one.
- Rename `custom` field for node metadata to `meta`.
- Move `icon` to `meta.icon`.
- Rename `normal_ui` to `default_ui`.
- Rename `filetypes` to `node_types`.
- Split `modes` into `modes.builtin` and `modes.custom`.
- Add the missing `create file` mode.
- Rename `focused_ui` to `focus_ui`.
- Make `general.table.header` non-nullable.
- Add support for incremental configuration updates.
Ref: https://github.com/sayanarijit/xplr/issues/45
Example:
```yaml
filetypes:
directory:
custom:
foo: bar
...
```
Where `foo` and `bar` can be anything string.
It can be accessed with the `{{{custom.foo}}}` variable.