refactor net code Generalize a bit the flow. Expect a request to be written and a body to be sended with net_send_ui. This will make easier to add other protocols like finger or gopher in the future. Also, switch to evbuffer instead of manually calling tls_read/write: with evbuffers we can abstract over the actual I/O routine and just read/write buffers in memory. This too will help with adding more protocols.

rename client -> net

rename gemini.c -> net.c