clean up unused includes

move unicode_isgraph in minibuffer.c (codepoint_isgraph)

remove unused unicode_isspace

move imsgev & co to their own file This avoids bringing the dependency on ev on telescope-identity(1) and the tests as well.

convert telescope to use ev instead of libevent libevent is a very cool library, I like the APIs and enjoy using it. However, telescope is not as large and doesn't have as many file descriptor, so libevent is quite ``too big'' for our needs. ev started as a small event loop on top of poll(2) for amused, and can be used here too, it just needed to grow the ability to handle several timers, as we need quite some on telescope (in fact, we use more timers than fds!)

remove imsg_borrow_str it's redundant due to ibuf_borrow_str()

send the reply code and meta in a single imsg

inline dispatch_imsg(); start to use some newer imsg api

work around macos lack of SOCK_CLOEXEC / SOCK_NONBLOCK rework mark_nonblock so it sets the cloexec flag too and use it in control.c to avoid these flags. (which are expected to become available on a future revision of POSIX and are already widely available.) It's not an issue for telescope to do the socket/accept + fcntl dance because there aren't threads that can fork(2) (there are no threads at all!) reported by @sikmir at github https://github.com/omar-polo/telescope/commit/59ef79dd19611c7846b00427e6f2267c748ae290#r74498414

replace has_prefix with strncmp

make imsg_event_add public

copy^W add IMSG_DATA_SIZE too

rename util.c -> utils.c for consistency