Add Pep8 Assembly language (#2070)

Pep/8 is a toy assembly language used in some universities for teaching
the basics of assembly and low-level programming.

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>

samples/Pep8/flag.pep

@@ -0,0 +1,23 @@
+_start:	LDA	0,i
+	LDX	0,i
+	LDA	20, i
+	ADDA	51, i
+	CPA	0,i
+	BRLT	s3
+	BR	s4
+s1:	LDBYTEA	s3, x
+	NOTA
+	STBYTEA s3, x
+	ADDX	1,i
+	CPX	12, i
+	BRNE	s1
+s2:	STOP
+s4:	LDA	31, d
+	LDX	50, d
+	RET0
+	STOP
+s3:	CPX	-27746, d
+	ANDX	-8241, i
+	SUBA	-12337, sxf
+	LDX	-12289, sx
+	.END