In crates where there was mixed information about source releases and
externals, some properties that apply only to the former were carried over to
the new externals-only manifest.
Also applied the rest of transformations described in alire#227: no top-level
[genera] table, name/version keys, [[depends-on]] array instead of table.
Crates without maintainer or pending migration remain in /orphaned
GitHub URLs rely on the default tarballs that at some point will
have to be released with uploaded binaries (with `alr publish` support).
Alejandro R. Mosteo
Pierre-Marie de Rodat