chore: update package.exclude list in Cargo.toml
It looks like this list hasn't been updated for new, removed, moved,
or renamed files in a while.
I've added all folders / files that are not useful for consumers of
the published crate to the "package.exclude" list.
This results in a reduction of the .crate file size by ~80%, from
1.24 MB to 205 kB.
Fabio Valentini