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.
I didn't write this!

But this is actually perfectly legal in both 2.7 and 3.x - `absolute_import` doesn't allow anything new, instead it _disallows_ relative imports which don't use the . syntax in this example.