Add tests for invalid (non-ascii) characters

lexer/invalid_utf8.invalid.mj

+/* Extracted from Markus Kuhn <http://www.cl.cam.ac.uk/~mgk25/> - 2015-08-28 - CC BY 4.0 */
+
+/* First continuation byte 0x80 */ €
+/* Last continuation byte 0xbf */ ¿
+
+/* 2 continuation bytes */ €¿
+/* 3 continuation bytes */ €¿€
+/* 4 continuation bytes */ €¿€¿
+/* 5 continuation bytes */ €¿€¿€
+/* 6 continuation bytes */ €¿€¿€¿
+/* 7 continuation bytes */ €¿€¿€¿€

lexer/overlong_ascii.invalid.mj

+/* Extracted from Markus Kuhn <http://www.cl.cam.ac.uk/~mgk25/> - 2015-08-28 - CC BY 4.0 */
+
+/* Overlong ASCII characters */
+/* U+002F = c0 af             */ 
+/* U+002F = e0 80 af          */ 
+/* U+002F = f0 80 80 af       */ 
+/* U+002F = f8 80 80 80 af    */ 
+/* U+002F = fc 80 80 80 80 af */ 

lexer/valid_utf8.invalid.mj

+public static void μαιν(String[] args) {}