Restructured according to review in pull request #567.
The "inputc" function was moved in slightly modified form
to kbhit.s and replaces the old keyboard scanner.
cgetc() uses the new kbhit() to read a character.
The way we want to use the INITBSS segment - and especially the fact that it won't have the type bss on all ROM based targets - means that the name INITBSS is misleading. After all INIT is the best name from my perspective as it serves several purposes and therefore needs a rather generic name.
Unfortunately this means that the current INIT segment needs to be renamed too. Looking for a short (ideally 4 letter) name I came up with ONCE as it contains all code (and data) accessed only once during initialization.
If kbhit() detects that a key is pressed, it fetches and
buffers the character. If cgetc() detects a buffered character,
this one is returned instead of fetching one with the PROM
routine.
