Allow disabling certificate verification

[tscs37]

For development purposes it can be useful to ignore certificate requirements (ie, expired certificates, mismatching hostnames, etc.)

It would be useful if the RequestBuilder had an option to disable Certificate Verification, something like danger_allow_invalid_certificates().

[sbstp]

Yes this is a something I wanted to do. I think it can be easily done by adding a parameter to the RequestBuilder i.e. attohttpc::get("https://localhost:8080").allow_insecure(true), something like this.

[sbstp]

This is out in 0.10.0