Make couch_dbdump able to get more things

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

Change-Id: I92b1fd0d696ee2f4e6b9b8f5d1c3b72bedd160f5
Reviewed-on: http://review.couchbase.org/33948
Reviewed-by: Ravi Mayuram <ravi@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>