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/stristack.pep

@@ -0,0 +1,50 @@
+main:		SUBSP	34, i
+		LDA	31, i
+		STA	0, s
+		CALL	fgets
+		ADDSP	2, i
+		CALL	ststro
+		STOP
+
+; Reads a string from stdin, stops reading when one of the following is true:
+;	- Read a \n
+;	- Read a maximum of `max` chars
+;
+; Parameters:
+;	- SP + 2: `max`, the maximum number of chars to read
+;	- SP + 4: `buffer` of length `max` + 1
+; Returns:
+;	void
+fgets:		LDX	0, i
+		LDA	0, i
+fgetslp:	CHARI	buffer, sx
+		LDBYTEA	buffer, sx
+		CPA	'\n', i
+		BREQ	fout
+		CPX	max, s
+		BREQ	fout
+		ADDX	1, i
+		BR	fgetslp
+fout:		LDA	'\x00', i
+		STBYTEA	buffer, sx
+		RET0
+max:	.EQUATE 2
+buffer: .EQUATE 4
+
+; Prints a string stored in stack
+;
+; Parameters:
+;	SP + 2: `string`
+; Returns:
+;	void
+ststro:		LDX	0, i
+		LDA	0, i
+strolp:		LDBYTEA	string, sx
+		CPA	'\x00', i
+		BREQ	strout
+		CHARO	string, sx
+		ADDX	1, i
+		BR	strolp
+strout:		RET0
+string: .EQUATE 2
+	.END