Add initial support for ARJ archives.
Document it.

We only support reading at the moment,
and only support the STORED (absense of) compression
with no encryption or multi-volume support.

Jira issue key: COMPRESS-226



git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1484246 13f79535-47bb-0310-9956-ffa450edef68