Add some basic regression tests.

Most cause crashes. Only macro-@ works correctly; the others need to
be fixed.

test/asm/test.sh

@@ -0,0 +1,7 @@
+fname=$(mktemp)
+
+for i in *.asm; do
+	../../rgbasm $i >$fname 2>&1
+#	diff -u $fname $(basename $i .asm).out
+	diff -u $fname ${i%.asm}.out
+done