[modules/datetime] Use parameter functionality to get format

Make the format string of the datetime module configurable using the new
parameter() method in the module.

Also, restructured the setting of the config information a bit so that
the parameter() method can be used in the constructor of a module.

see #23

bumblebee/engine.py

@@ -25,8 +25,11 @@ class Module(object):
     (e.g. CPU utilization, disk usage, etc.) derive from
     this base class.
     """
-    def __init__(self, engine, widgets):
+    def __init__(self, engine, config={}, widgets=[]):
         self.name = self.__module__.split(".")[-1]
+        self._config = config
+        if not "name" in self._config:
+            self._config["name"] = self.name
         self._widgets = []
         if widgets:
             self._widgets = widgets if isinstance(widgets, list) else [widgets]
@@ -41,13 +44,8 @@ class Module(object):
 
     def parameter(self, name, default=None):
         """Return the config parameter 'name' for this module"""
-        name = "{}.{}".format(self._config_name, name)
-        return self._config.get(name, default)
-
-    def set_config(self, config, name):
-        """Set the config for this module"""
-        self._config = config
-        self._config_name = name
+        name = "{}.{}".format(self._config["name"], name)
+        return self._config["config"].get(name, default)
 
 class Engine(object):
     """Engine for driving the application
@@ -76,9 +74,10 @@ class Engine(object):
             module = importlib.import_module("bumblebee.modules.{}".format(module_name))
         except ImportError as error:
             raise bumblebee.error.ModuleLoadError(error)
-        res = getattr(module, "Module")(self)
-        res.set_config(self._config, config_name)
-        return res
+        return getattr(module, "Module")(self, {
+            "name": config_name,
+            "config": self._config
+        })
 
     def running(self):
         """Check whether the event loop is running"""