[modules/cpu] Add configurable warning and critical thresholds

The cpu module now has cpu.warning and cpu.critical thresholds. If the
CPU utilization is higher than any of those values, the widget's state
changes to warning or critical, respectively.

see #23

bumblebee-status

@@ -18,19 +18,19 @@ def main():
         inp=inp,
     )
 
-    try:
-        engine.run()
-    except KeyboardInterrupt as error:
-        inp.stop()
-        sys.exit(0)
-    except bumblebee.error.BaseError as error:
-        inp.stop()
-        sys.stderr.write("fatal: {}\n".format(error))
-        sys.exit(1)
-    except Exception as error:
-        inp.stop()
-        sys.stderr.write("fatal: {}\n".format(error))
-        sys.exit(2)
+    engine.run()
+#    try:
+#    except KeyboardInterrupt as error:
+#        inp.stop()
+#        sys.exit(0)
+#    except bumblebee.error.BaseError as error:
+#        inp.stop()
+#        sys.stderr.write("fatal: {}\n".format(error))
+#        sys.exit(1)
+#    except Exception as error:
+#        inp.stop()
+#        sys.stderr.write("fatal: {}\n".format(error))
+#        sys.exit(2)
 
 if __name__ == "__main__":
     main()