Enable next line of user input to be sent to the local function 'fun'
as an argument. The input line will not be parsed by the driver.
Note that input_to is non-blocking which means that the object calling
input_to does not pause waiting for input. Instead the object contin‐
ues to execute any statements following the input_to. The specified
function 'fun' will not be called until the user input has been col‐
lected.
If "input_to()" is called more than once in the same execution, only
the first call has any effect.
If optional argument 'flag' is non-zero, the line given by the player
will not be echoed, and is not seen if snooped (this is useful for col‐
lecting passwords).
The function 'fun' will be called with the user input as its first
argument (a string). Any additional arguments supplied to input_to will
be passed on to 'fun' as arguments following the user input.