Get rid of struct data and change the prototypes.

This commit removes the data struct that was defined in leornian.h and
used in the in() and out() function pointer prototypes passed to leo().

This change was made so that files wishing to implement in() and out()
for a later leo() call need no include leornian.h. Specifically, a
planned future daemon using a plugin structure to modularly define in()
and out() functions will benefit from this.