Moving "sub" libraries to their own repositories

From: Glen Fernandes (glen.fernandes_at_[hidden])
Date: 2023-03-08 20:07:21

We have (very) few cases where within a repository we have more than one
library inside a repository. One example is boostorg/functional whose
meta/libraries.json has:

- functional
- functional/factory
- functional/forward
- functional/overloaded_function

See: https://github.com/boostorg/functional/blob/master/meta/libraries.json

What do we think about having separate repositories for the last three
above? e.g.  The second one would be boostorg/functional_factory

Some might be better collapsed into the first library (i.e. become part of
just "functional").

We haven't been allowing this for newer libraries, but it would be nice to
remove it from these few existing cases too.

Ultimately meta/libraries.json in each library repository would have just
one  library entry.

Glen