[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/xrandr.py

@@ -1,89 +0,0 @@
-import bumblebee.module
-import bumblebee.util
-import re
-import os
-import sys
-import subprocess
-
-def description():
-    return "Shows all connected screens"
-
-def parameters():
-    return [
-    ]
-
-class Module(bumblebee.module.Module):
-    def __init__(self, output, config):
-        super(Module, self).__init__(output, config)
-
-        self._widgets = []
-
-    def toggle(self, event, widget):
-        path = os.path.dirname(os.path.abspath(__file__))
-        toggle_cmd = "{}/../../bin/toggle-display.sh".format(path)
-
-        if widget.get("state") == "on":
-            bumblebee.util.execute("{} --output {} --off".format(toggle_cmd, widget.get("display")))
-        else:
-            neighbor = None
-            for w in self._widgets:
-                if w.get("state") == "on":
-                    neighbor = w
-                    if event.get("button") == 1:
-                        break
-    
-            if neighbor == None:
-                bumblebee.util.execute("{} --output {} --auto".format(toggle_cmd,
-                    widget.get("display")))
-            else:
-                bumblebee.util.execute("{} --output {} --auto --{}-of {}".format(toggle_cmd,
-                    widget.get("display"), "left" if event.get("button") == 1 else "right",
-                    neighbor.get("display")))
-
-    def widgets(self):
-        process = subprocess.Popen([ "xrandr", "-q" ], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-        output, error = process.communicate()
-
-        widgets = []
-
-        for line in output.split("\n"):
-            if not " connected" in line:
-                continue
-            display = line.split(" ", 2)[0]
-            m = re.search(r'\d+x\d+\+(\d+)\+\d+', line)
-
-            widget = bumblebee.output.Widget(self, display, instance=display)
-            widget.set("display", display)
-
-            # not optimal (add callback once per interval), but since
-            # add_callback() just returns if the callback has already
-            # been registered, it should be "ok"
-            self._output.add_callback(module=display, button=1,
-                cmd=self.toggle)
-            self._output.add_callback(module=display, button=3,
-                cmd=self.toggle)
-            if m:
-                widget.set("state", "on")
-                widget.set("pos", int(m.group(1)))
-            else:
-                widget.set("state", "off")
-                widget.set("pos", sys.maxint)
-
-            widgets.append(widget)
-
-        widgets.sort(key=lambda widget : widget.get("pos"))
-
-        self._widgets = widgets
-
-        return widgets
-
-    def state(self, widget):
-        return widget.get("state", "off")
-
-    def warning(self, widget):
-        return False
-
-    def critical(self, widget):
-        return False
-
-# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4