minibuffer: augment minibuffer_read with the initial input fixes a regression where the text inputted via ui_read() can't be edited.

minibuffer: redesign enter_minibuffer and fix regression use a struct to pass the arguments to enter_minibuffer since they're so many. While here, also allow to pass a printf(3)-like format string for the prompt and specify the initial input. Also, fix a regression: if we don't set vline.cplen we can't properly handle the input, so do that in enter_minibuffer to avoid having to fix all the callers.

make yornp data be a void pointer instead of a tab

minibuffer: pass the string to the donefn() This avoids the callback to have to use the (private) minibuffer_compl_text() to get the string. It'll simplifies a follow-up changes, too.

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.