Support for Chat Mauve Mode

Added monochrome and color DHGR initialization depending on the
horizontal resolution. 560x192x1 images are displayed in JACE without
color fringes. Should be tested with real hardware.

DISPLAY.S

@@ -98,14 +98,22 @@ DEBUT     BIT $C050      ; GRAPHIQUES
           STA DHGR
           LDA SOURCE+$0E
           CMP #$18
-          BNE DHGRINI
-          LDA SOURCE+$0F
-          CMP #$01
-          BNE DHGRINI
-          JMP GSTEST
-DHGRINI   BIT $C05E      ; DOUBLE HR
-          STA $C00D      ; 80 COLONNES
-          STA $C001      ; SET80STORE
+          BEQ GSTEST
+
+          STA $C00C
+          BIT $C05E      ; DOUBLE HR
+          STA $C05F
+          STA $C05E
+          STA $C05F
+          STA $C00D
+          STA $C05E
+          CMP #$30
+          BEQ MONO
+          STA $C05F
+          STA $C05E
+          STA $C05F
+          STA $C05E
+MONO      STA $C001      ; SET80STORE
           BIT $C055      ; PAGE2
           LDA #01
           STA DHGR