Enable settings conversion to CAF

[mavam]

No description provided.

[dominiklohmann]

Mostly fine by me except for one small, subtle issue in the code.

Please change the test record for the unit test such that it contains a list that contains at least one different type, e.g., record.

I did not test this locally; the unit tests running through cover this functionality quite well.

[dominiklohmann]

Approving as is, just one remark/question: Why did you move from caf::settings to caf::dictionary<caf::config_value>? The former is an alias of the latter, but I find caf::settings to be the more idiomatic type to enable conversion to.

[mavam]

Why did you move from caf::settings to caf::dictionary<caf::config_value>?

The reason is that caf::settings is just a top-level alias. The real recursive structure is a config_value and this is what I'd like the user of the API to remember: a config_value can contain a dictionary of config_values. Since the recursion occurs in the implementation, I find it cleaning to stick to a single set of vocabulary.