add utils.h, forgot in recent commits

link the thfr@ article about OOTB-TOFU in the ACKNOWLEDGEMNTS section

add to CAVEATS a note about the naive text-wrapping algorithm

tweak cache-info message

fringes already have a prefix of "~"

crank up cache limits 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.

document cache-info

drop useless struct 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.

timer-based cache removal: delete cached pages older than 15 minutes

simplify load_url_in_tab

sync changelog

add cache-info

cache: keep track of the total size and number of cached pages

mcache_tab: free previous copies of that page

rename util.c -> utils.c for consistency