[modules/time] Add parameter for format string

Format string for strftime is now configurable. Also, changed the
separator for module name vs. arguments to "::" to make it possible to
have ":" as part of the strftime format string (which is useful in most
cases).

Eventually, I'll probably have to come up with a better way, i.e. a
fully-fledged parser, and move away from "special characters", but right
now, the effort seems too much for the gain.

bumblebee/modules/time.py

@@ -3,9 +3,10 @@ import bumblebee.module
 
 class Module(bumblebee.module.Module):
     def __init__(self, args):
+        self._fmt = args[0] if args else "%x %X"
         super(Module, self).__init__(args)
 
     def data(self):
-        return datetime.datetime.now().strftime("%x %X")
+        return datetime.datetime.now().strftime(self._fmt)
 
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