Added support for samesite cookie attribute.
Added support for samesite cookie attribute.

Same-site cookies allow servers to mitigate the risk of CSRF attacks.

Enabled by default in:
	Chrome 51
	Opera 39
	Firefox

More information in:
https://www.chromestatus.com/feature/4672634709082112
https://www.sjoerdlangkemper.nl/2016/04/14/preventing-csrf-with-samesite-cookie-attribute/

PerfectlySoft/Perfect-HTTP