REPL "status" command outputs incorrect shard statistics & does not use "shard" info

[jondgoodwin]

There are two issues here:

• When outputting shard-specific statistics, it uses corpus-wide document and posting count numbers rather than shard-specific numbers. This causes it to output four wrong statistics, including the incorrectly calculated values for shard-specific document bit-size and bits per posting. To fix this, the shards must keep track of their own document and posting count statistics, which can then be retrieved and properly used by the status command.
• The status command currently accepts an optional shard number on the command (with 0 as the default). It needs to be modified to use the min/max shard info gathered by the shard command.