prevent telescope from dying when connecting to non-tls/non-gemini servers (found by trying to load a bogus ``gemini://gemini.nytpu.com'' -- the correct url for the capsule is ``gemini://nytpu.com'')

Changelog since 0.1.1: * save certificates per (host, port) tuple, not only per-host * don't crash on invalid lines in known_hosts * allow saving the new certificate after mismatch * fix cmd_scroll_down/up: they scrolled two line more than what intended * fix out-of-bound * automatic gemini:// on load-url * display a `!' when a non-focused tab gets loaded * added aliases for tab-{next,new,previous} * unbreak forward-char * debounce resize event * new heuristic to obtain the page title: if no h1 found, try with h2s and h3s * ask the user to save a page when it can't be rendered * drop the urgent flag when switching to a tab after closing one * fix tab width

it's good for thing like images and text with weird encodings.