Adjust grammar so that it never depends on newline tokens

doc/parser_grammar.txt

@@ -1,6 +1,6 @@
 /* string literals are lexer identifier tokens with that particular value */
 <program>   ::= <statement>*
-<statement> ::= ( <label> | <directive> | <instruction> ) <newline>
+<statement> ::= <label> | <directive> | <instruction>
 
 <label> ::= <identifier> <colon>