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/Function.py

@@ -0,0 +1,49 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+"""A function that can be specified at the command line, with an argument."""
+
+import importlib
+import re
+
+MATCHER = re.compile(r'([\w.]+)(.*)')
+
+def _split_function(desc):
+    m = MATCHER.match(desc)
+    if not m:
+        raise ValueError('"%s" is not a function' % desc)
+    name, args = (g.strip() for g in m.groups())
+    args = eval(args or '()')  # Yes, really eval()!
+    if not isinstance(args, tuple):
+        args = (args,)
+    return name, args
+
+class Function(object):
+    def __init__(self, desc='', default_path=''):
+        self.desc = desc.strip()
+        if not self.desc:
+            # Make an empty function that does nothing.
+            self.args = ()
+            self.function = lambda *args, **kwds: None
+            return
+
+        self.function, self.args = _split_function(self.desc)
+        if '.' not in self.function:
+            if default_path and not default_path.endswith('.'):
+                default_path += '.'
+            self.function = default_path + self.function
+        p, m = self.function.rsplit('.', 1)
+        try:
+            mod = importlib.import_module(p)
+        except:
+            raise ValueError('Can\'t find Python module "%s"' % p)
+
+        try:
+            self.function = getattr(mod, m)
+        except:
+            raise ValueError('No function "%s" in module "%s"' % (p, m))
+
+    def __str__(self):
+        return self.desc
+
+    def __call__(self, *args, **kwds):
+        return self.function(*(args + self.args), **kwds)