[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/modules/battery.py

@@ -1,52 +0,0 @@
-import datetime
-import bumblebee.module
-import os.path
-
-def description():
-    return "Displays battery status, percentage and whether it's charging or discharging."
-
-def parameters():
-    return [ "battery.device: The device to read from (defaults to BAT0)" ]
-
-class Module(bumblebee.module.Module):
-    def __init__(self, output, config):
-        super(Module, self).__init__(output, config)
-        self._battery = config.parameter("device", "BAT0")
-        self._capacity = 100
-        self._status = "Unknown"
-
-    def widgets(self):
-        self._AC = False;
-        self._path = "/sys/class/power_supply/{}".format(self._battery)
-        if not os.path.exists(self._path):
-            self._AC = True;
-            return bumblebee.output.Widget(self,"AC")
-
-        with open(self._path + "/capacity") as f:
-            self._capacity = int(f.read())
-        self._capacity = self._capacity if self._capacity < 100 else 100
-
-        return bumblebee.output.Widget(self,"{:02d}%".format(self._capacity))
-
-    def warning(self, widget):
-        return self._capacity < self._config.parameter("warning", 20)
-
-    def critical(self, widget):
-        return self._capacity < self._config.parameter("critical", 10)
-
-    def state(self, widget):
-        if self._AC:
-            return "AC"
-
-        with open(self._path + "/status") as f:
-            self._status = f.read().strip()
-
-        if self._status == "Discharging":
-            status = "discharging-{}".format(min([ 10, 25, 50, 80, 100] , key=lambda i:abs(i-self._capacity)))
-            return status
-        else:
-            if self._capacity > 95:
-                return "charged"
-            return "charging"
-
-# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4