Pause print on GPIO filament runout sensor

The following needs to be added to the config.yaml:

  filament:
    pin: XX
    bounce: 400
    gpioOptions: 0
    pauseOptions: 0

Option Descriptions:

• pin = The GPIO Pin in BCM mode, so for pin 26, you'd enter 7 (for GPIO7)
• bounce = The time to wait for the switch to settle, in ms.
• gpioOptions = Configure the default GPIO pull_up_down mode. 0 [default] is PULL_DOWN mode. 1 is for PULL_UP mode.
• pauseOptions = Configure the pause action. 0 [default] pauses immediately. 1 waits for the next ZChange event (layer change).

An API is available to check the filament sensor status via a GET method to /plugin/filament/status which returns a JSON

• {status: "-1"} if the sensor is not setup
• {status: "0"} if the sensor is OFF (filament not present)
• {status: "1"} if the sensor is ON (filament present)

The status 0/1 depends on the type of sensor, and it might be reversed if using a normally closed switch.

A build using an optical switch can be found at http://www.thingiverse.com/thing:1646220

Note: Needs RPi.GPIO version greater than 0.6.0 to allow access to GPIO for non root and chmod a+rw /dev/gpiomem. This requires a fairly up to date system.