Add https cert and key options to docker

Docker-DCO-1.1-Signed-off-by: Colin Rice <colin@daedrum.net> (github: discordianfish)
Add https example

Docker-DCO-1.1-Signed-off-by: Colin Rice <colin@daedrum.net> (github: discordianfish)
Simplified https example

The prior example wasn't working for me.

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Refactor client methods to stop code duplication

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add basic https client support

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add custom (self-signed) root ca support

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add client certificate authentication support

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Disable "bind to public IP" warning if TLS enabled

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Updated documentation and added a complete example

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add prelimited https integration tests

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add support for non-authenticated TLS

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add documentation of tls flags

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Set tls flag defaults and add -tlsverify

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Replace httputil.ClientConn by http.Client

httputil.ClientConn has to be closed which means we would have to
carry around a reference to it because resp.Body.Close won't close it.

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)