Kernel/LibC: Implement basic epoll

This implementation is on top of inodes instead of fds as linux does it.
If I start finding ports/software that relies on epoll allowing
duplicate inodes, I will do what linux does.

I'm probably missing multiple epoll_notify's which may cause hangs but
the system seems to work fine :dd:

kernel/include/kernel/FS/Pipe.h

@@ -40,6 +40,7 @@ namespace Kernel
 		virtual bool can_read_impl() const override { return m_buffer_size > 0; }
 		virtual bool can_write_impl() const override { return true; }
 		virtual bool has_error_impl() const override { return false; }
+		virtual bool has_hangup_impl() const override { return m_writing_count == 0; }
 
 	private:
 		Pipe(const Credentials&);