GUI: Slider

The slider displays on the right of the screen, with two buttons OK and Cancel by default.

Compact syntax is

boolean slider(&myLCD, value)

with true when OK pressed, and false when Cancel pressed. 

The value is updated if OK is pressed.

Extensive syntax with all optional parameters is

boolean slider(Serial_LCD * lcd0, uint16_t &value, 
uint16_t min=0, uint16_t max=511, uint16_t step=8, 
uint16_t minColour0=greenColour, uint16_t maxColour0=redColour, 
String okText0="OK", uint16_t okTextColour0=whiteColour, uint16_t okColour0=blueColour, 
String cancelText0="Cancel", uint16_t cancelTextColour0=whiteColour, uint16_t cancelColour0=yellowColour);