feat(buzbee): implement terminal echo and backspace handling

src/buzbee.s

@@ -48,10 +48,14 @@ INPLOOP
   beq NOCHAR@
   cmpa #$1B            ; ESC?
   beq HESC@            ;  Handle ESC
+  cmpa #$08            ; BS?
+  beq HBACKSPC@        ;  Backup a char
   cmpa #$0D            ; CR?
   beq EXIT@            ;  Then parse input buffer
   cmpy #BBIN_DEPTH     ; Are we at the end of the input buffer?
   beq FULLBUF@         ; Handle the buffer being full
+ECHO@
+  jsr POUTCHAR         ; Echo char back, this includes BS chars
   sta BBIN_BASE,y      ; Add it to the input buffer
   leay 1,y
 NOCHAR@
@@ -81,6 +85,11 @@ HESC@
   jsr POUTCHAR
   ldy #$0000           ; On return we cmpy #$0000 and if eq then newline.
   rts
+HBACKSPC@
+  clrb                 ; Clear last char
+  leay -1,y
+  stb BBIN_BASE
+  bra ECHO@            ; Echo the char in A
 FULLBUF@
   lda #$07             ; ASCII BEL
   jsr POUTCHAR