Add support for requests parameters verify and cert

[tosinator]

I have been using Daedalus as my cardano-wallet provider. Daedalus uses HTTPS with custom CA and client certificates. In order to be able to use them properly, we need to pass "verify" and "cert" parameters to requests library. This patch accomplishes that.

I'm not sure if I need to consider anything else (I used this library only for a little). If not a direct contribution to code, hopefully this at least serves as a feature request.

Thanks!