Improved keyboard control

[mkraska]

Hello,

I tried your software on a Raspi with a numeric keypad as jogging device and a standard 7" touch screen
I understand that keyboard jogging isn't within the original design intent. Yet I would propose the following improvements:

• Instead of just reacting on keypress events I propose to start jogging at keypress and stop jogging at keyrelease. While keypressed, send move commands with increasing feed rate and distance (just like Grbl Overseer) but short enough to have good response to keyrelease.
• Alternatively, use a variable step with configurable initial value and range of values, use +/- to select from the values, e.g. [ 0.1, 1, 10 ]
• Avoid hitting the limits by reading the Grbl settings and checking the moves against the limits.
• It seems that SetZero requires multiple keypress events to really get the work coordinates to zero.