Defines action to take on button press (on the old devkit 0.9), button connected to GPIO 16.
This function is only available if the firmware was compiled with DEVKIT_VERSION_0_9 defined.
#### Syntax
`node.key(type, function())`
#### Parameters
-`type`: type is either string "long" or "short". long: press the key for 3 seconds, short: press shortly(less than 3 seconds)
-`function`: user defined function which is called when key is pressed. If nil, remove the user defined function. Default function: long: change LED blinking rate, short: reset chip