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.

bin/ripple/util/File.py

@@ -0,0 +1,7 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import os
+
+def normalize(f):
+    f = os.path.join(*f.split('/'))  # For Windows users.
+    return os.path.abspath(os.path.expanduser(f))