This reintroduces support for Go modules, as v4.
CloseNotifier() is removed as it has been obsoleted, see https://golang.org/doc/go1.11#net/http
It was already NOT working (not sending signals) as of 1.11 the functionality was gone, we merely
deleted the functions that exposed it. If anyone still relies on it they should migrate to using
`c.Request().Context().Done()` instead.
Closes#1268, #1255
In HTTPSRedirect and similar middlewares, determining if redirection is
needed using `c.IsTLS()` causes redirect loop when an application is running
behind a TLS termination proxy, e.g. AWS ELB.
Instead, I believe, redirection should be determined by
`c.Scheme() != "https"`. This works well even behind a TLS termination proxy.
