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+. 

Unfortunately, this is not correct.  Indeed, NONE of these things are available in Python 2.7 without the import.  :-D

Try this demo in your favorite Python 2.7 interpreter (I didn't include a demo of absolute import, you'll have to trust me.)
    >>> 2 / 3
    0
    >>> print 5
    5
    >>> type('a')
    <type 'str'>
    >>> from __future__ import absolute_import, division, print_function, unicode_literals
    >>> 2 / 3
    0.6666666666666666
    >>> type('a')
    <type 'unicode'>
    >>> print 5
      File "<stdin>", line 1
        print 5
              ^
    SyntaxError: invalid syntax
    >>> 

My plan is to support 2.7 and "3.x" - the `from __future__ ...` clause is necessary to do that.  In these first exploratory phases I'm only actually testing in 2.7.