Show primary key for item tables

Changes:
- in table:show, if the table is an item table,
  show the primary key field with primary key
  name and type;
- in table:list, if at least one of the table is
  an item table, show the primary key column in the
  table view, or show the primary key field in the
  JSON,CSV,TSV formats only for item tables.
Show support for msgpack.gz in the command description