replace is_null with isset for better performance

ref: [is-null docs](http://php.net/manual/en/function.is-null.php#84161)
formart with tab
Fix string newline escaping for Windows

As per discussion in #164, this allows strings with `\\n` and `\\n\r` before the string delimiter.
Merge remote-tracking branch 'yahasana/patch-1'
Merge remote-tracking branch 'caiosm1005/patch-1'