Ensure a newline exists at the end of files.

Fixes #42.

regexp.go

@@ -300,6 +300,9 @@ func (r *RegexLexer) Tokenise(options *TokeniseOptions, text string) (Iterator,
 	if options == nil {
 		options = defaultOptions
 	}
+	if !r.config.DontEnsureNL && !strings.HasSuffix(text, "\n") {
+		text += "\n"
+	}
 	state := &LexerState{
 		Lexer:          r,
 		Text:           []rune(text),