gg: add support for client certs

customizable servname & verbose + misc tweaks * add -H for explicit servname (for SNI) * add -v to print also the request * misc tweaks: move *flag variables to global scope (initialisation to 0 for free!) and explicit handshake.

reuse the same buffer for the request and response

handle TLS_WANT_POLL{IN,OUT} libtls doesn't seem to return when doing blocking I/O, but libretls does every single time.

don't alter the struct iri

add gg, a barebones Gemini client