delete pages that are older than one hour, and scan the cache only once every five minutes. The previous defaults were a bit too much conservative.

instead of keeping the struct mcache that's private to mcache.c and used only once, just define its fields as (static) variables. While here, mark as static also gemtext_prefixes.

it's not spelled `util.h' because otherwise it'd get included instead of /usr/include/util.h

- don't expose the evbuffer where we store the cached page - cache to/from tabs instead of buffers

the idiom if (load_next_page(...)) start_loading_anim(...); is fundamentally wrong because `load_next_page' (or previous page, or anything else that call into load_url) *may* load all the page before returning (thanks to the cache, but not only, cf. load_page_from_str.) Instead, let's call start_loadign_anim at the start of make_request so it's always called in the right moment. Cache and other special pages don't end up calling make_request anyway, and we already call stop_loading_anim when a request finishes (or fails.) move start_loading_anim up in make_request.