- Disabled the solar incidence calculation for pvoutput.org
- The inverter internal teperature is now exposed in PVoutput's
  "Power Used" parameter.
- Added a function that controls an external cooling device. The
  behaviour is implemented as a Schmitt-trigger, and is controled by the
  following configuration parameters:

  fan_temp_low    => 35.0,
  fan_temp_high   => 40.0,
  fan_cmd_off     => <commandline utility to switch cooling device on>
  fan_cmd_on      => <commandline utility to switch cooling device on>