Implements HTTPS proxy functionality

Do not timeout when WriteControl deadline is zero

perf: reduce timer in write_control

perf: reduce timer in write_control

Fix typos

Handle errcheck warnings

Handle net.Error Temporary() deprecation

Move doHandshake to client.go

Improve bufio handling in Upgrader.Upgrade

Use crypto/rand for mask key

Return 426 status on missing upgrade header

Unbundle x/net/proxy and update to recent version

Silence false positive lint warning in proxy code

Added tests for subprotocol selection

Fixes subprotocol selection (aling with rfc6455)