[core] Refactor engine

This is going to be a bit more comprehensive than anticipated. In order
to cleanly refactor the core and the engine, basically start from
scratch with the implementation.

Goals:

* Test coverage
* Maintain backwards compatibility with module interface as much as
  possible (but still make modules easier to code)
* Simplicity

see #23

bumblebee/engine.py

@@ -1,38 +0,0 @@
-import importlib
-import bumblebee.theme
-import bumblebee.output
-import bumblebee.config
-import bumblebee.modules
-
-class Engine:
-    def __init__(self, config):
-        self._modules = []
-        self._config = config
-        self._theme = bumblebee.theme.Theme(config)
-        self._output = bumblebee.output.output(config)
-
-    def load_module(self, modulespec):
-        name = modulespec["name"]
-        module = importlib.import_module("bumblebee.modules.{}".format(name))
-        cfg = bumblebee.config.ModuleConfig(self._config, name, modulespec["alias"])
-        obj = getattr(module, "Module")(self._output, cfg)
-        obj.register_callbacks()
-        return obj
-
-    def load_modules(self):
-        for m in self._config.modules():
-            self._modules.append(self.load_module(m))
-
-    def run(self):
-        self._output.start()
-
-        while True:
-            self._theme.begin()
-            for m in self._modules:
-                self._output.draw(m.widgets(), self._theme)
-            self._output.flush()
-            self._output.wait()
-
-        self._output.stop()
-
-# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4