We used to return nil, nil if the token didn't exist.
We now return os.ErrNotExist.

Signed-off-by: Sebastien Binet <binet@cern.ch>

We used to test AutoSubgroups before upgrading the description,
which would break handling of the (obsolete) AllowSubgroups
field.

Thanks to David Saulpic.

This avoids a crash in the VP8 parser.

The former don't properly unwrap errors.

We now create the server and the listener in the calling thread,
and only create a new goroutine before calling server.Serve.

The previous way depended on implementation details
of GetConfiguration.

Allow reading and modifying description files, in a manner
that aligns with the needs of the API.

The "stats.json" file is moved under "galene-api", where the rest
of the API will live.

The "users" entry is now a dictionary mapping user names to
passwords and permissions.  In order to allow for wildcards,
there is a new type of password, the wildcard password, and
an extra array called "fallback-users".

The field "allow-anonymous" no longer exists, this is now
the default behaviour.  The field "allow-subgroups" has been
renamed to "auto-subgroups".

We provide backwards compatibility for group definition files,
but not for the config.json file, where the old "admin" array
is simply ignored.