postprocessd 0.2.1

* Make postprocessd binary compatible with the Megapixels api fully
* Force the background daemon to process all pictures sequentially to
  limit cpu and memory use when taking multiple pictures in sequence
* fully daemonize the postprocessd background process so Megapixels
  doesn't wait on it
* End the background process once the queue is done.
* Add Megapixels scripts in the postprocessor.d directory