Add support for :FD-HANDLER communication style to ECL backend

[nickg]

Also tested with NIL and :SPAWN communication styles.

[luismbo]

@dkochmanski any chance you could review this?

[dkochmanski]

mmm, ECL has pink label :-)

PR looks fine to me at first glance, but SLIME having preferred communication set to :fd-handler doesn't start REPL which I could use on ECL 16.1.3 (tried only this version so far). I've removed FAS from ~/.slime directory and things got compiled anew, but it didn't help.

[nickg]

@dkochmanski you need to run something like (loop (serve-event:serve-all-events)) to actually get it to process the events.

My use case is running a SWANK server inside a program with a single-threaded event loop that I then slime-connect to from Emacs. I'm not sure if there's a way to get Emacs to call serve-all-events itself when it starts the inferior-lisp?

[luismbo]

@nickg perhaps you could add a note about this to https://common-lisp.net/project/slime/doc/html/Communication-style.html#Communication-style?