Ability to accept self-signed certificates

[Sir-Photch]

I have this edge use case where I need to accept self-signed certificates for a https connection.
Supporting this is possible with the https-native feature since crate::native_tls::TlsConnector::Builder facilitates this by calling danger_accept_invalid_certs(true).

I am not sure how you would like to see this integrated that's why I kept it to a hacked local git clone instead of creating a PR, but is this something you can see this library to support?

[neonmoe]

I'd rather not, both since more advanced use-cases might as well use a more fully featured http crate, and to try and avoid creating security issues by minimizing the amount of messing with tls stuff.