Uses the 'self-pipe trick' to catch and process signals outside of the signal environment. A few XXX remains, but this is good enough to hit the tree.

Move there functions that relies on the global event loop.

Allow to create custom event loops, but still retain the possibility to just use a global one.

ev::any was just to save some typing; not sure it's worth it. Can be easily confused with ev::READ and ev::WRITE.

I actually don't get the difference between def and const. maybe def is guaranteed to be a compile-time constant (just guessing). Other "#defines" in the hare stdlib seem to use def tho, so follow here too.

avoids issues with adding/removing elements from the 'working' queue. ev::add and ev::del only touch the "wip" queue, while poll only touches the "working" queue. This technically has the consequences that if from event A we remove event B which is pending and not yet processed, we may still fire B once.

This was intended as an optimization: poll returns the number of elements in the pollfd set which had events. Can be revised in the future.