strip comments from the parse tree

I dunno if I'll like this decision in the long run, but we'll try it.

parse.go

@@ -40,10 +40,14 @@ func (p *parser) next() token {
 		p.backup = p.backup[:len(p.backup)-1]
 		return t
 	}
+SKIP_COMMENTS:
 	t, ok := <-p.input
 	if !ok {
 		return token{t_eof, "eof"}
 	}
+	if t.t == t_comment {
+		goto SKIP_COMMENTS
+	}
 	return t
 }