Re-export some things at the top level

[YaLTeR]

Not sure what yet, but I guess at least libdisplay_info::info::Info would make sense to re-export.

[cmeissl]

libdisplay-info is structured into some kind of modules and I tried to keep it the same for this wrapper.
The only official entry point at the moment is by using the "High-Level API" with libdisplay_info::info::Info,
so I guess it makes sense to include it in the top-level lib. For the rest it makes more sense to require users
to explicit refer to the modules imo.