[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/nic.py

@@ -1,62 +0,0 @@
-import netifaces
-import bumblebee.module
-
-def description():
-    return "Displays the names, IP addresses and status of each available interface."
-
-def parameters():
-    return [
-            "nic.exclude: Comma-separated list of interface prefixes to exlude (defaults to: \"lo,virbr,docker,vboxnet,veth\")"
-    ]
-
-class Module(bumblebee.module.Module):
-    def __init__(self, output, config):
-        super(Module, self).__init__(output, config)
-        self._exclude = tuple(filter(len, self._config.parameter("exclude", "lo,virbr,docker,vboxnet,veth").split(",")))
-
-    def widgets(self):
-        result = []
-        interfaces = [ i for i in netifaces.interfaces() if not i.startswith(self._exclude) ]
-        for intf in interfaces:
-            addr = []
-            state = "down"
-            try:
-                if netifaces.AF_INET in netifaces.ifaddresses(intf):
-                    for ip in netifaces.ifaddresses(intf)[netifaces.AF_INET]:
-                        if "addr" in ip and ip["addr"] != "":
-                            addr.append(ip["addr"])
-                            state = "up"
-            except Exception as e:
-                addr = []
-            widget = bumblebee.output.Widget(self, "{} {} {}".format(
-                intf, state, ", ".join(addr)
-            ))
-            widget.set("intf", intf)
-            widget.set("state", state)
-            result.append(widget)
-
-        return result
-
-    def _iswlan(self, intf):
-        # wifi, wlan, wlp, seems to work for me
-        if intf.startswith("w"): return True
-        return False
-
-    def _istunnel(self, intf):
-        return intf.startswith("tun")
-
-    def state(self, widget):
-        intf = widget.get("intf")
-
-        iftype = "wireless" if self._iswlan(intf) else "wired"
-        iftype = "tunnel" if self._istunnel(intf) else iftype
-
-        return "{}-{}".format(iftype, widget.get("state"))
-
-    def warning(self, widget):
-        return widget.get("state") != "up"
-
-    def critical(self, widget):
-        return widget.get("state") == "down"
-
-# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4