Allow HTTPs requests to sites with self-signed certificates

[oxcafedead]

I heavily use nvim with your awesome plugin for the daily work, and sometimes I need to make requests to the internal webapps which work via TLS with self-signed certs.
That plugin for VS code, which is mentioned as the main "inspiration" for this one, by default accepts self-signed certs.

Maybe this is not ideal from the security reasons, but it would be a good thing to have this at lest configurable:

• default behavior, check certs as is now
• set an additional list of custom CAs
• do not check certs at all