Support no_proxy

HTTP::Tiny uses proxy if user sets `http_proxy` environment value.
But user wants not use proxy for some hosts, such as localhost, hosts in LAN.
In such case, some applications(eg. curl, wget) use `no_proxy` or `NO_PROXY` environment value.
I implemented it to HTTP::Tiny. If user sets `no_proxy` environment value, it is comma-separated
list of hosts, HTTP::Tiny does not use proxy for these hosts. User can also set hosts not used proxy
by constructor.

Please review this patch.