New command line LedgerTool (RIPD-243).

* Retrieve and process summary or full ledgers.
* Search using arbitrary criteria (any Python function).
* Search using arbitrary formats (any Python function).
* Caches ledgers as .gz files to avoid repeated server requests.
* Handles ledger numbers, ranges, and special names like validated or closed.
Not sure what version of python we're using, but all of these things are available natively in 2.6+. I really hope we're not using 2.5 which is thoroughly antique and unsupported by upstream developers.