Renamed INITBSS to INIT and INIT to ONCE.

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.

libsrc/c16/cgetc.s

@@ -56,7 +56,7 @@ L2:     jsr     KBDREAD         ; Read char and return in A
         .constructor    initkbd
         .destructor     donekbd
 
-.segment        "INIT"
+.segment        "ONCE"
 
 .proc   initkbd