Add test for HIGH() and LOW()

It compares the results of the operators with the expected result if
doing the same thing manually.

Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>

test/link/high-low-a.asm

@@ -0,0 +1,22 @@
+ldhilo : MACRO
+    ld  HIGH(\1),LOW(\2)
+ENDM
+
+SECTION "r0", ROM0[$0]
+ld HIGH(af),a
+ld HIGH(bc),LOW(bc)
+ld LOW(bc),HIGH(bc)
+ld HIGH(de),LOW(de)
+ld LOW(de),HIGH(de)
+    ldhilo hl, hl
+ld LOW(hl),HIGH(hl)
+
+db HIGH(label+$AB)
+db LOW(label+$AB)
+
+db HIGH($1234)
+db LOW($1234)
+
+SECTION "o",OAM
+DS $10
+label: