Make couch_dbdump able to get more things available

This fixes MB-10102, MB-10019, MB-10103 and satisfies some requests
from the support team.

Specifically added are:

 * Can look up a specific key
 * Can dump all local documents or a specific local doc
 * Fixed --byid sort option being ignored
 * Local doc dump and regular dump can output data as machine-readable
   JSON
 * Can dump document bodies as hex (if document is binary data)
 * Show document physical (disk) and actual (uncompressed) size.
 * More useful help message

[Dave Rigby]: Forward-ported to 3.0 branch from 2.5.1.
    Original SHA: de0dcdc292935b93c4700386c5f65c92daff7039
    Original gerrit: http://review.couchbase.org/33948

Change-Id: I447fe670ed4edbc9b841050ae11a0848cd440830
Reviewed-on: http://review.couchbase.org/37187
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>