Move signal handling to libuv event loop

This removes all signal handling code from os_unix.c to os/signal.c. Now signal
handling is done like this:

- Watchers for signals are registered with libuv default event loop
- `event_poll` continuously calls `poll_uv_loop` to produce events until it
  receives user input, SIGINT or a timeout
- Any signals received in `poll_uv_loop` will push events to a queue that is
  drained and processed by `event_poll`

Signals aren't handled directly in the libuv callback to avoid recursion in the
event loop(which isn't supported by libuv).

The same principle will apply to other events in the future: Push to a queue
from a libuv callback and drain it from `event_poll`

1 files changed, 0 insertions, 3 deletions

diff --git a/src/normal.c b/src/normal.c
index 0646a62fcf..6319e19203 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -7480,9 +7480,6 @@ static void nv_open(cmdarg_T *cap)
     n_opencmd(cap);
 }
 
-
-
-
 /*
  * Trigger CursorHold event.
  * When waiting for a character for 'updatetime' K_CURSORHOLD is put in the