Enhancements for cursor calculation

Fix handling of newlines.
Wrap around to top of screen when newline occurs
in last line.
Initialize screen width in crt0.s.

libsrc/c1p/cputc.s

@@ -44,14 +44,12 @@ L3:     iny
         rts
 
 newline:
-        lda     SCR_LINELEN     ; xsize-1
-        sec                     ; Account for -1 above
-        adc     SCREEN_PTR
-        sta     SCREEN_PTR
-        bcc     L4
-        inc     SCREEN_PTR+1
-L4:     inc     CURS_Y
-        rts
+        inc     CURS_Y
+        lda     CURS_Y
+        cmp     #24             ; screen height 25 lines hardcoded
+        bne     plot
+        lda     #0              ; wrap around to line 0
+        sta     CURS_Y
 
 plot:   ldy     CURS_Y
         lda     ScrLo,y

libsrc/c1p/crt0.s

@@ -13,6 +13,7 @@
 .import    zerobss, initlib, donelib
 
 .include  "zeropage.inc"
+.include  "extzp.inc"
 
 ; ---------------------------------------------------------------------------
 ; Place the startup code in a special segment
@@ -26,6 +27,13 @@ _init:    LDX     #$FF                 ; Initialize stack pointer to $01FF
           TXS
           CLD                          ; Clear decimal mode
 
+; ---------------------------------------------------------------------------
+; Initialize screen width
+; TODO: Can initialization be done in a more idiomatic way?
+; TODO: Create function for changing screen width
+          LDA     #$18
+          STA     SCR_LINELEN
+
 ; ---------------------------------------------------------------------------
 ; Set cc65 argument stack pointer