Update get_active_service documentation

=item $status->get_active_service

Returns a hashref describing the active service when a service is active and

nothing otherwise. The hashref contains the keys B<url> (URL to the station

board service), B<stopfinder> (URL to the stopfinder service, if supported),

B<name>, and B<productbits> (arrayref describing the supported modes of

transport, may contain duplicates).

nothing otherwise. The hashref contains the following keys.

=over

=item B<name> => I<string>

service name, e.g. Bay Area Rapid Transit or Deutsche Bahn.

=item B<mgate> => I<string>

HAFAS backend URL

=item B<languages> => I<arrayref>

Languages supported by the backend; see the constructor's B<language> argument.

=item B<productbits> => I<arrayref>

MOT bits supported by the backend. I<arrayref> contains either strings

(one string per mode of transit) or arrayrefs (one string pair per mode of

transit, with the first entry referring to the MOT identifier and the second

one containing a slightly longer description of it).

=back

=item Travel::Status::DE::HAFAS::get_services()

Returns an array containing all supported HAFAS services. Each element is a

hashref and contains all keys mentioned in B<get_active_service>.

It also contains a B<shortname> key, which is the service name used by

the constructor's B<service> parameter.

the constructor's B<service> parameter, e.g. BART or DB.

=item Travel::Status::DE::HAFAS::get_service(I<$service>)