Add "On pin P0 down" input

[gquintana]

There is a "On pin P0 pressed" input which waits for P0 to go up then down:

1  _  
0_| |_

There is a "On pin P0 released" input which waits for P0 to go down:

1_  
0 |_

I'd like to have an input "On pin P0 down" input which waits for P0 to go up:

1  _  
0_| 

To compare with JavaScript browser events: there are 3 key events: keydown, keyup and keypressed (=keydown+keyup)

[abchatra]

Closing this as we tracking the issue in #963