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/osic1p/cgetc.s

@@ -11,7 +11,7 @@
         .include        "zeropage.inc"
 
 ; Initialize one-character buffer that is filled by kbhit()
-        .segment        "INIT"
+        .segment        "ONCE"
 initcgetc:
         lda     #$00
         sta     CHARBUF         ; No character in buffer initially