Make sure a function to recursively merge dictionaries is accessible and documented

[frank-lenormand]

This request might not require any effort to fulfil, I haven’t checked the code.

Recursively merging Python dictionaries is an (ever) unsolved problem, on the side of the standard library.

Confight deals with dictionaries, and the community could benefit from its dictionary merging capabilities.

For example:

from confight import merge_dictionaries
merge_dictionaries(defaults, user_config)

Make sure the function is exported and documented.