Feature Request: let `from_kwargs` accept higher-level names with full Option value

[schlichtanders]

currently, from_kwargs and related methods only accept leaf values. However sometimes it is handy to overwrite whole subset by specifying the entire Option value for the subtree.

[Roger-luo]

I don't quite remember why it didn't but it seems to be a good idea to me. Currently yeah it flattens all the keyword argument so that you can update things inner.