Add support for DOAP "package" metadata

While scanning the same archive as in #2254 and https://github.com/nexB/scancode-toolkit/issues/2258#issuecomment-701024567 from https://www.apache.org/dyn/closer.cgi?path=/kafka/2.6.0/kafka-2.6.0-src.tgz there is are a few package manifest that are ignored:
- a build.gradle (See #793 )
- a DOAP rdf file at doap_Kafka.rdf (see attached
[doap_Kafka.rdf.txt](https://github.com/nexB/scancode-toolkit/files/5302155/doap_Kafka.rdf.txt) )

We should be able to collect package data from such a file:
```rdf

2014-04-12

Apache Kafka


Apache Kafka is a distributed, fault tolerant, publish-subscribe messaging.
A single Kafka broker can handle hundreds of megabytes of reads and writes per second from thousands of clients. Kafka is designed to allow a single cluster to serve as the central data backbone for a large organization. It can be elastically and transparently expanded without downtime. Data streams are partitioned and spread over a cluster of machines to allow data streams larger than the capability of any single machine and to allow clusters of co-ordinated consumers. Kafka has a modern cluster-centric design that offers strong durability and fault-tolerance guarantees. Messages are persisted on disk and replicated within the cluster to prevent data loss. Each broker can handle terabytes of messages without performance impact.



Scala









Jun Rao

```