Inspired by Werkzeug but improved. Related to #539 and #598.
The "access_route" property supports:
1. derive addrs from "Forwarded" header (defined by RFC7239)
2. derive addrs from "X-Forwarded-For" header
3. derive addrs from "X-Read-IP" header
4. or derive addr from WSGI "REMOTE_ADDR" header
The "remote_addr" property is a shortcut of WSGI "REMOTE_ADDR" header
Thanks to all the code review and advices from @MackYoel and @kgriffs.