add cmd_search to search using a search engine This adds a new command `search', bound by default to `s', that prompts for a query and loads and consult the ``oracle'' (the search engine) using default_search_engine (which will be made customizable.) It also temporarly supports only gemini URLs. Feature requested by -fab-, thanks!

load and optionally remember client certificates This adds use-certificate, a user function to start using a certificate or switch to a different one. It asks whether to persist the certificate, if not it will only be used for the current session. use-certificate is implicitly called when the server replies with a 6x status code.

move includes back to the root directory Splitting stuff into sub-directories was just a big mistake.