This changes the prototype of uv_run() from:
int uv_run(uv_loop_t* loop);
To:
int uv_run(uv_loop_t* loop, uv_run_mode mode);
Where `mode` is UV_RUN_DEFAULT, UV_RUN_ONCE or UV_RUN_NOWAIT.
Fixes#683.
Remove the next_watcher and replace it with a linked list. Said list is named
endgame_handles (because the uv-win calls it that) and contains all the handles
that are in the UV_CLOSING state.
The goal of this commit is two-fold:
a) remove a dependency on libev, and
b) share more code with uv-win in the future
A nice side effect is that it shaves a few bytes off a uv_handle_t.