wldbg: add apostrophe to client's name in a message
wldbg: use signalfd for catching signals

This won't interrupt message handling in the middle and
we can easily replace the default handler by some other handler from
passes
wldbg: handle epoll more generically

add wldbg_monitor_fd function which will add the fd to epoll
and as data sets structure

struct wldbg_fd_callback {
	int fd;
	void *data;
	int (*dispatch)(int fd, void *data);
};

In program we can then define this structure and use it for
arbitrary purpose - we can handle wayland messages and signals form
signalfd the same way. Also passes can add/replace these if they
have a handler. Moreover, the code is more structuralized and easier
to manage

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>