I mean that writing config files programmatically not necessary enough and should not part of this library.
I don't understand that point of view: any application (as opposed to simple command line utility) you write will almost certainly want to both read and write it's configuration : take a look at your favorite word processor/speadsheet/photo editor and I bet you it does exactly that.
Any application is overstatement IMO. For the application have a need to save some parameters there should be a way to change them during application runtime. This fact limit our scope to something with GUI (with rare exclusions). These application indeed may need bidirectional access to permanent storage for some date. But I would use Serialization library for this purpose. Why would I need to go through extra hoops with parameters tree? Gennadiy